How do I sort Table1 in Descending Order by clicking on the column heading

private testContext db = new testContext();
public List<Table1> thistable = new List<Table1>();
[HttpPost]
public ActionResult Index(int Idt)
{
    var sortthistable = from s in db.Data1 select s;
    sortthistable = sortthistable.OrderByDescending(s => s.Idt);
    thistable = sortthistable.ToList();
    return View(thistable);
 }

@Html.ActionLink("Idt", "Index")