Unable to route through Area

HI All,

Please can anyone help using Area Routing which is not working using ASP.NET Core 3.1

HTML Code

<div class="row"><div class="col-12">
        @Html.DropDownList("NationCase", (SelectList)ViewBag.NationList, "Select nation", new
{ onchange = "document.location.href =  '/' + this.options[this.selectedIndex].value;", @class = "form-control form-control-sm col-sm-3 mb-1", @style = "float:left;" })</div></div

C#

  [Area("Admin")]
    public class WebController : Controller
    {

        private readonly GlobalDBContext _context;


        public WebController(GlobalDBContextcontext)
        {
            _context = context;            
        }

        public IActionResult Index()
        {
            getNationList(null);
            return View();
        }


        [Route("/{id}")]
        public IActionResult Index(int id)
        {
            ViewBag.LocID = id;
            getNationList(id);
            return View();
        }




        private void getNationList(int? id)
        {
            var nationList = _context.NationMeterTop.Select(s => new { Id = s.LocationId, Value = s.Nation }).OrderBy(s => s.Value).ToList();
            ViewBag.NationList = new SelectList(nationList, "Id", "Value", id);
        }
    }

Startup.cs

  app.UseEndpoints(endpoints =>
            {
                endpoints.MapAreaControllerRoute(
                    name: "MyAreaAdmin",
                    areaName: "Admin",
                    pattern: "Admin/{controller=Home}/{action}/{id?}");

             
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Home}/{action=Index}/{id?}");
            });

I want when user select value from dropdown it should below action method

[Route("/{id}")]
        public IActionResult Index(int id)
        {
            ViewBag.LocID = id;
            getNationList(id);
            return View();
        }

Thanks,

Shabbir