Getting Data from a POST or GET form Request

Hello, i am using Arduino Wifi rev 2 with the DHT11 sensor!

The whole idea is to show a web page when someone is connected in the arduino wifi and control a fan and get temperature and humidity sensor values.

Everything is working fine except one thing, i have made a form in which i have an input of type rage and i want via that form to control a value named fanthreshold on the Arduino.

I have been trying for a while now with no luck on how to get the value from the form request.

here is the code i have

#include <WiFiNINA.h>
#include <dht.h>
#include <SPI.h>
#include <SD.h>

dht DHT; // creates a DHT object

int sensor =  A2;
int fan = 3;
boolean fanstatus = false;
boolean manual = true;
int fanthreshold = 25;

int card = 4;

char ssid[] = "Ptixiaki";        // network SSID (name)

int status = WL_IDLE_STATUS;
WiFiServer server(80);

String header;

void setup() {
  Serial.begin(9600);
  pinMode(fan, OUTPUT);

  if (!SD.begin(card)) {
    Serial.println("Card failed, or not present");
   } 
  else {
    Serial.println("card initialized.");
  }
  
  status = WiFi.beginAP(ssid);
  if (status != WL_AP_LISTENING) {
    Serial.println("Creating access point failed");

    while (true);
  }

  delay(1000);

  server.begin();
}

void saveSensorData()
{
  int chk = DHT.read11(sensor); // Starts reading from the DHT11 sensor

   float t = DHT.temperature; // Gets the values of the temperature
   float h = DHT.humidity; // Gets the values of the humidity

            
   File dataFile = SD.open("data.txt", FILE_WRITE);
            
    if (dataFile) {  
          dataFile.println("Temperature: ");
          dataFile.print(t);
          dataFile.println("");

               
          dataFile.println("Humidity: ");
          dataFile.print(h);
          dataFile.println("");
               
          dataFile.close(); 
         } else {
           Serial.println("There was an error with the sd card.");
         }
}

void loop()
{
  
  WiFiClient client = server.available();
  
 // saveSensorData();
  
 // Serial.println("Sensor Data was written on the card");
  
 // delay(2000);
  
  if (client) {                             // if you get a client,
    Serial.println("new client");           // print a message out the serial port
    String currentLine = "";                // make a String to hold incoming data from the client
    while (client.connected()) {            // loop while the client's connected
      if (client.available()) {             // if there's bytes to read from the client,
        char c = client.read();             // read a byte, then
        header += c;                        // print it out the serial monitor
        if (c == '\n') {                    // if the byte is a newline character


          if (currentLine.length() == 0) {

            client.println("HTTP/1.1 200 OK");
            client.println("Content-type:text/html");
            client.println("Connection: close");
            client.println();

            // Display the HTML web page
            client.println("<!DOCTYPE html><html>");
            client.println("<head><meta name=\"viewport\" content=\"width=device-width, initial-scale=1\">");

            client.println("<meta HTTP-EQUIV=\"refresh\" content=\"4\">");
            client.println("<link rel=\"icon\" href=\"data:,\">");

            client.println("<style>html,body { font-family: Arial; margin: 0px; padding:0px; background-color: #e2e4e7;}");
            client.println(".button { background-color: #00b1b3; border: none; color: white; padding: 5px 15px;");
            client.println("text-decoration: none; font-size: 16px; margin: 2px; cursor: pointer;border-radius:10px;}");
            client.println(".none { pointer-events: none; opacity: 0.5;}");
            client.println("</style></head>");

            client.println("<body><div style=\"text-align:center;background-color:#fff; padding:30px 20px;font-size: 20px;\">Temp and Humidity Readings</div>");

            int chkData = DHT.read11(sensor); // Starts reading from the DHT11 sensor

            float t = DHT.temperature; // Gets the values of the temperature
            float h = DHT.humidity; // Gets the values of the humidity
            
            client.println("<h4 id=\"temp\" style=\"text-align:center;\">Temperature: ");
            client.print(t, 1);
            client.println("</h4>");

            client.println("<h4 id=\"hum\" style=\"text-align:center;\">Humidity: ");
            client.print(h, 0);
            client.println("</h4>");

            client.println("<h5>New Reading in: <span id=\"timer\">4</span></h5>");
            client.println("<h5>Fan Threshold: ");
            client.print(fanthreshold);
            client.println("</h5>");

            // ========================== Manual - Auto ===========================================
            client.println("<div style=\"text-align:center; margin-bottom: 30px;\">");

            if (manual == true) {
              client.println("<a href=\"/Manual\"\"><button class=\"button none\">Manual</button></a>");
            } else {
              client.println("<a href=\"/Manual\"\"><button class=\"button\">Manual</button></a>");
            }

            if (manual == false) {
              client.println("<a href=\"/Auto\"\"><button class=\"button none\">Auto</button></a>");
            } else {
              client.println("<a href=\"/Auto\"\"><button class=\"button\">Auto</button></a>");
            }
            client.println("</div>");


            // ========================== Manual - FORM ===========================================
            if (manual == true) {
              client.println("<div style=\"background-color: #fff; padding:10px;\">");
            } else {
              client.println("<div class=\"none\" style=\"background-color: #fff; padding:10px;\">");
            }

            client.println("<div style=\"text-align:right;\">");

            if (fanstatus == true) {
              client.println("<a href=\"/ON\"\"><button class=\"button none\">Start Fan</button></a>");
            } else {
              client.println("<a href=\"/ON\"\"><button class=\"button\">Start Fan</button></a>");
            }

            if (fanstatus == false) {
              client.println("<a href=\"/OFF\"\"><button class=\"button none\">Stop Fan</button></a>");
            } else {
              client.println("<a href=\"/OFF\"\"><button class=\"button\">Stop Fan</button></a>");
            }
            client.println("</div>");

            //========================== FORM ===========================================
            client.println("<form action=\"/\" method=\"POST\"");
            client.println("<h3>Temp");
            client.println("<output name=\"tempOutputName\" id=\"tempOutputId\">24</output>");
            client.println("</h3>");
            client.println("<input type=\"range\" min=\"20\" max=\"35\" name=\"tempInputName\" id=\"tempInputId\" value=\"24\" style=\"width:100%\" oninput=\"tempOutputId.value = tempInputId.value\">");

            client.println("<button class=\"button\" type=\"submit\">Submit</button>");
            client.println("</form>");

            client.println("</div>");


            //========================== JS Scripts ======================================
            client.println("<script>");
            client.println("var counter = 4;setInterval(function(){counter--;document.getElementById('timer').innerHTML = counter;},1000);");
            client.println("</script");

            client.println("</body></html>");


            client.println();
            // break out of the while loop:
            break;
          }
          else {
            currentLine = "";
          }
        }
        else if (c != '\r') {
          currentLine += c;
        }

        if (currentLine.endsWith("GET /ON"))
        {
          digitalWrite(fan, HIGH);
          fanstatus = true;
        }

        if (currentLine.endsWith("GET /OFF"))
        {
          digitalWrite(fan, LOW);
          fanstatus = false;
        }

        if (currentLine.endsWith("GET /Manual"))
        {
          manual = true;
        }

        if (currentLine.endsWith("GET /Auto"))
        {
          manual = false;
        }


      }
    }
    // close the connection:
    client.stop();
  }

  
  
}

Looking for someone that can help me out on how to get the value of the input field