assigning ramdom numbers for all existing user

Question

I have register 5 users in my app. I need assigning ramdom number for all of them but I cant I have no idea how to do that. It´s Like a temporary PIN for authentication. I have that code but only create the number , not insert the number to users

 

 

 

public ActionResult Test(User user)
     {

         Random rand = new Random();
         int numero = rand.Next(1, 10000);
         var model = new User();


         model.UserId = user.UserId;
         model.Nombre = user.Nombre;
         model.Codigo = numero;


         db.Users.Add(model);
         db.SaveChanges();
         return View(model);

     }