#include <Servo.h>

Servo servo1;  // create servo object to control a servo

int position = 0;    // variable to store the servo position

void setup() {
  servo1.attach(9);  // attaches the servo on pin 9 to the servo object
}

void loop() {
  for (position = 0; position <= 180; position += 1) { // rotate from 0 degrees to 180 degrees
   // in steps of 1 degree
    servo1.write(position);                   // tell servo to go to position in variable 'pos'
    delay(18);                          // waits Xms for the servo to reach the position
  }

  for (position = 180; position >= 0; position -= 1) { // rotate from 180 degrees to 0 degrees
    servo1.write(position);                   // tell servo to go to position in variable 'pos'
    delay(18);                          // waits Xms for the servo to reach the position
  }
}
//reference https://maker.pro/arduino/projects/servo-motor-on-virtual-arduino-online-simulator