Clean Up Level

using UnityEngine.SceneManagement;

public class LevelManager
{
    static LevelManager _instance;

    public static LevelManager Instance
    {
        get
        {
            return _instance ??= new LevelManager();
        }
    }

    public void LoadNextLevel()
    {
        var currentLevel = SceneManager.GetActiveScene().buildIndex;
        if (currentLevel + 1 >= SceneManager.sceneCountInBuildSettings)
        {
            currentLevel = -1;
        }

        SceneManager.LoadScene(currentLevel + 1);
    }
}

using UnityEngine;

public class Exit : MonoBehaviour
{
    void OnTriggerEnter2D(Collider2D other)
    {
        LevelManager.Instance.LoadNextLevel();
    }
}