Where would I call the DoDestroyOnLoad function on my Singleton Script

I need to load my scene . The singleton script is attach to a UI text . I gotten an error when I have the destroyonload. Here is my script :

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class GameManagerSingleton : MonoBehaviour
public static GameManagerSingleton instance = null;

 public static int score;

 private Text text;
 void Awake()
	 text = GetComponent <Text> ();
	 score = 0;
     if (instance != null && instance != this)
         Destroy(gameObject);    // Ensures that there aren't multiple Singletons

     instance = this;

 void Update()
	text.text = "Score: " + score;
	 Debug.Log("Score: " + score);


Use Unity Wiki Singleton Script

You will not have to take care of anything.