I made an levelcontroller in c# but it always goes back to level 2 does someone know how to fix this?

Everytime i start a level that is not level 1 i automatically go back to level 2 and when i start at level 2 i have to do it twice but i want players to choose wich level they want to start. here is the code: public class LevelController : MonoBehaviour { private static int _nextLevelIndex = 1; private Enemy[] _enemies;

 private void OnEnable()
 {
     _enemies = FindObjectsOfType<Enemy>();
 }

 void Update()
 {
    foreach(Enemy enemy in _enemies)
     {
         if (enemy != null)
             return;
     }

     Debug.Log("You killed all enemies");

     _nextLevelIndex++;
     string nextLevelName = "Level" + _nextLevelIndex;
     SceneManager.LoadScene(nextLevelName);
 }