I would like to return the Z block, if z block is chosen then, the user should have 3 chances to change the block

 string GerRandomLetters(){
     int randomLetters = Random.Range (1, 8);//getting random numbers to swich

     string randomLettersName = "Prefabs/Letter_J"; //setting default

     switch (randomLetters) { //switching the numbers
         
     case 1:
         randomLettersName = "Prefabs/Letter_J";
         break;
     case 2:
         randomLettersName = "Prefabs/Letter_L";
         break;
     case 3:
         randomLettersName = "Prefabs/Letter_long";
         break;
     case 4:
         randomLettersName = "Prefabs/Letter_S";
         break;
     case 5:
         randomLettersName = "Prefabs/Letter_square";
         break;
     case 6:
         randomLettersName = "Prefabs/Letter_T";
         break;
     case 7:
         randomLettersName = "Prefabs/Letter_Z"; 
         if (Input.GetKeyDown (KeyCode.Space)) {//if user presses the space

             for (int i = 0; i < 3; i++) {//user can change 3times
                 int randomLettersSecond = Random.Range (1, 7);

                 string randomblockName = "Prefabs/Letter_J";

                 switch (randomLettersSecond) {

                 case 1:
                     randomblockName = "Prefabs/Letter_J";
                     break;
                 case 2:
                     randomblockName = "Prefabs/Letter_L";
                     break;
                 case 3:
                     randomblockName = "Prefabs/Letter_long";
                     break;
                 case 4:
                     randomblockName = "Prefabs/Letter_S";
                     break;
                 case 5:
                     randomblockName = "Prefabs/Letter_square";
                     break;
                 case 6:
                     randomblockName = "Prefabs/Letter_T";
                     break;
                 }

                 return randomblockName; //returning the second switch

             }
             break;
     
         }
         return randomLettersName; //returning the main switch
     }
 }