How to set my score to 0 when hit restart ;

I tried to do that resetting the score from playerprefmanager in the scenecontroller and in game manager but it's not working neither ways .

   private void Start()
     {
         Scene scene = SceneManager.GetActiveScene();
         Debug.Log("Active Scene is '" + scene.name + "'.");
         nextSceneToLoad = SceneManager.GetActiveScene().buildIndex + 1;
         highScore = PlayerPrefs.GetInt(PlayerPrefManager.HIGH_SCORE);
         ResetScore();
     }
     private void Awake()
     {

     {
         SetUpSingleton();
     }

 }
 private void SetUpSingleton()
 {
     int numberGameSessions = FindObjectsOfType<GameSession>().Length;
     if (numberGameSessions > 1)
     {
         Destroy(gameObject);
     }
     else
     {
         DontDestroyOnLoad(gameObject);
     }
 }


 private void Update()
 {
     if (SceneManager.GetActiveScene().buildIndex == 1)
     {
         ResetScore();
     }
     if (score > highScore)
     {
         highScore = score;

         PlayerPrefs.SetInt(PlayerPrefManager.HIGH_SCORE, highScore);

     }
     Debug.Log("to achive score '" + (levelScore * nextSceneToLoad) + "'.");

     if (score>=(levelScore * nextSceneToLoad))
      {

         LoadNextScene();
         nextSceneToLoad = SceneManager.GetActiveScene().buildIndex + 1;


     }
     PlayerPrefs.SetInt(PlayerPrefManager.SCORE, score);       
 }
 public int GetScore()
 {
     return score;
 }
 public void AddPoints(int amount)
 { 
     score += amount;
   
 }
   

 public void LoadNextScene()
 {
     SceneManager.LoadScene(nextSceneToLoad);


 }
 void ResetGame()
 {
     Destroy(gameObject);
 }

 void ResetScore()
 {
     PlayerPrefs.SetInt(PlayerPrefManager.SCORE, 0);
 }

}