• LED on 16 pin
• press boot before upload

#include <Arduino.h>
 
void setup() {
  Serial.begin(115200); 
  pinMode(16, OUTPUT);
}
 
void loop() {
  static int zzz = 0;
  Serial.println(zzz++);
 
  digitalWrite(16, HIGH);
  delay(1000);
  digitalWrite(16, LOW);
  delay(1000);      // wait for a second
}

https://www.instructables.com/id/ESP32-With-Battery-Holder/