This is the code for the power-on of sim7600e:

/**************************Power on Sim7x00**************************/
void Sim7x00::PowerOn(int PowerKey = powerkey){
   uint8_t answer = 0;

  Serial.begin(9600);

  // checks if the module is started
  answer = sendATcommand("AT", "OK", 2000);
  if (answer == 0)
  {
    Serial.print("Starting up...\n");
    
    pinMode(PowerKey, OUTPUT);
    // power on pulse
    digitalWrite(PowerKey, HIGH);
    delay(500);
    digitalWrite(PowerKey, LOW);
    
    // waits for an answer from the module
    while (answer == 0) {     // Send AT every two seconds and wait for the answer
      answer = sendATcommand("AT", "OK", 2000);
	  delay(1000);
    }

Source: Sim7600 and arduino won’t connect – Using Arduino / Project Guidance – Arduino Forum