The referenced script on this Behaviour is missing

I know this is a common question, but I still haven’t find an answer for it. So basically I attach this script to a 2D object

using System.Collections;
using System.Collections.Generic;
using UnityEngine.SceneManagement;
using UnityEngine;

public class SwitchScene : MonoBehaviour {
	 public string level = "testingscene2";

	// Use this for initialization
	void TriggerEnter2D (Collision2D Colider){

		         if(Colider.gameObject.tag == "Player")
                          SceneManager.LoadScene(sceneName: "Platformer2");
	void Start () {
	// Update is called once per frame
	void Update () {

I’m trying to make it so that when the player touches this object, the scene will change. But so far the only result I have got is “The referenced script on this Behavior is missing”. And when I checked out the script in the inspector, I got " The associated script can not be loaded. Please fix any compile errors and assign a valid script ". What seems to be the problem here?

This usually happens when you delete or rename a script outside Unity.
You can probably fix it by selecting the gameobject with the missing behavior and replacing the missing behavior with your SwitchScene script.