How to make player distinguish between individual enemies

In my game enemies are spawned in a straight line and the quantity of them is determined by the current level. After my player is done battling one enemy, he needs to move to the next enemy in line.
What would be the best way to execute this in my game?
Right now I am considering assigning a number to each enemy and have they player move towards the next number up, but I do not know how to program this.

Current enemy spawner script:

public class EnemySpawner : MonoBehaviour
    public GameObject EnemyPrefab;
    public Transform PlayerTransform;

    private float spawnZ = 0f;
    private float spawnDistance = 15f;
    private int enemyNumber;
    void Start()
        enemyNumber = PlayerPrefs.GetInt("level", 1) * 3;

        for (int i = 0; i < enemyNumber; i++)

    void SpawnEnemy()
        GameObject go;
        go = Instantiate(EnemyPrefab) as GameObject;
        go.transform.position = new Vector3(0, 0, spawnZ);
        spawnZ += spawnDistance;


you could store your enemies as a List<T>:

Every time a battle begin, get a enemy gameobject with index=0 from list to battle it. When this battle is done, remove theindex=0item from list and start a new battle. Loop it and until list’s count becomes 0.