How to have a modal popped up after a post controller has submitted, should I create a new controller for it? Im new to asp.net

Question

here i have my LogIn Controller where if the log in is successful then a modal should pop up which will prompt the user to select mood:

[HttpPost]
public ActionResult LogIn(User u)
{
    var user = _userRepo.Table.Where(model => model.Username == u.Username && model.Password == u.Password).FirstOrDefault();
    try
    {
        if (_userRepo.Table.Where(model => model.Username == u.Username).FirstOrDefault().Password != u.Password)
        {
            ModelState.AddModelError("", "Invalid password");
            ViewBag.LoginSuccess = false;
            return View();
                }
        }
        catch (NullReferenceException)
        {
        ModelState.AddModelError("", "User not exist");
                ViewBag.LoginSuccess = false;
                return View();
        }
        catch (TargetException)
        {
        ModelState.AddModelError("", "User not exist");
                ViewBag.LoginSuccess = false;
                return View();
        }

    FormsAuthentication.SetAuthCookie(u.Username, false);
    ViewBag.LoginSuccess = true;
    Session["User"] = user;

    //return RedirectToAction("Register");
    return RedirectToAction("../UsersPage/ChooseMood");

again if log in was succssful, a modal should pop up instanly which will prompt user to select mood before proceeding to this controller:

public ActionResult UsersHome(string mood)
{
    if (User.Identity.IsAuthenticated)
    {
        return PartialView((User)Session["User"]);
        } else
        {
        return View("../Home/Index");
        }
}

what should be my approach? should I create new controller for the choose mood(modal pop up) then redirect to that UserHome controller?