How to store a number

Hi all , im busy with sim 800l module , i have the module working and can send and recieve sms. I want to change the senders number in the code via serial terminal. i have a basic sketch writen but i cant get it to work. Ï also tried to save the "readString " to eeprom but had no luck with that to. Can any one please help with this problem, I also searched the net for a solution but got more confused
Thanks

#include <SoftwareSerial.h>
#include <EEPROM.h>
 #include <Sim800l.h>
Sim800l Sim800l;
String readString;
int addr = 0;
char* text;
char* number;
bool error; //to catch the response of sendSms
String val =readString;
 
void setup()
{
   Sim800l.begin();
   Serial.begin(9600);
 
   while (!Serial.available())
   { 
      Serial.println("Type Cellphone number and press enter");  
      delay (500);
  }
  while (Serial.available()) {
    char c = Serial.read();  //gets one byte from serial buffer
    readString += c; //makes the string readString
    delay(2);  //slow looping to allow buffer to fill with next character
  }

    if (readString.length() > 0) {
    Serial.print(readString);
    }  
    readString=""; //empty for next input
 } 
   


void loop()
{

  text="test";  //text for the message. 
  number= readString;        //change to a valid number.
  error=Sim800l.sendSms(number,text);
  delay(2000);
  Serial.flush();
  delay(55000);
}