C# Foreach element[,] in list problem

Hello, so Im working on a BoardGame, and I would to do an actions (Damage them in this case) to all the piece/servant (they have the script Servant attached to them) that has a certain condition (all the ally in this case) on the board, so I have FindAllAlly () that finds all the ally servants, but I cant figure out how to use the list (how to do an actions to all the Servants[i,j] in the list. Here is the script that I tried to use :

 public Servant[,] Servants{ set; get; } 
 
 public List FindAllAlly () {

     List<Servant[,]> allyServants = new List<Servant[,]> ();
     for (int i = 0; i < tileNum; i++) {
         for (int j = 0; j < tileNum; j++) {
             if (Servants [i, j] != null) {        // si il y a un personnage
                 if (Servants [i, j].isPlayer == GameManager.Instance.isPlayerTurn) {
                     allyServants.Add(Servants [i, j]);
                 }
             }
         }
     }
     return allyServants;
 }

 private void TestServant (){
     List<Servant[,]> list = FindAllAlly ();

     foreach (Servant [,] testServants in list) {
         testServants.TakeDamage ( 5) // TakeDamage is on Servant script, but I cant use it, it isnt in the suggestions after typing "." so I guess it isnt getting the Servant script ? 
     }
 }

Looked on the forums about Lists and how to use them but couldnt find any answers or didnt know that I found it. What am I doing wrong ?