DeathMenu.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement; // Add this line for SceneManager

public class DeathMenu : MonoBehaviour
{
    public string mainMenuLevel;

    public void RestartGame()
    {
        FindAnyObjectByType<GameManager>().Reset();
       // GameManager.instance.RestartGame();
    }

    public void QuitToMain()
    {
        SceneManager.LoadScene(mainMenuLevel); // Replace Application.LoadLevel with SceneManager.LoadScene
    }
}