How to get URL parameters?

So I'm using the Arduino Nano combined with a Pretzel Board where I'm running on a NanoESP() Webserver. I'm already successfully running a dynamic html site on the Arduino.

I'm currently also able to send data from the Arduino to the client using "esp.sendData(id, data)" but how am I able to make data transfer working in the other direction?

I probably want to make use of URL Parameters but how can the Arduino Webserver can read them out. Is there any function implemented?

 loop() {
  String method, ressource, parameter;
  int id;
  if (http.recvRequest(id, method,ressource,parameter) {
   if (ressource = "/") { 
    http.sendFromFlash(id, index, sizeof(index));
    if (esp.findUntil("?data=", "\n")) {
      Serial.println("not working");