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);
  }
 
 

}