Complete tutorial : https://help.sinric.pro/pages/tutorials/custom-device-types/alcohol-sensor/MQ-3.html

mq4.ino

#if defined(ESP8266)
  const int adcPin = A0;  
#elif defined(ESP32) 
  const int adcPin = 34;  
#elif defined(ARDUINO_ARCH_RP2040)
  const int adcPin = 26;  
#endif

int sensorVal;

void setup() {
 Serial.begin(9600);
 Serial.println("warming up for 20 seconds ..!");
 delay(20000);
}

void loop() {
 sensorVal = analogRead(adcPin);
 Serial.printf("value: %d\r\n", sensorVal);
 delay(2000); // delay 2s
}