Filter record with DropDownList in ASP.Net MVC

There is a table of products, each product has a group, for example (Fruit, Cereal, Beverage).

I want to create a search box with a dropdown list.

When a fruit is selected in the dropdown list, I want it to change instantly and list the Fruits.

Thanks

@Html.DropDownList("GRUP", (List<SelectListItem>)ViewBag.grup, "", new { })
<button class="btn btn-secondary">Ara</button> 

public ActionResult Urunler(int? id, int? kimlik)
{
    var ad = (string)Session["FIRMAKODU"];
    ViewBag.firma = ad;
    var plasiyerid = (string)Session["PLASIYERID"];
    ViewBag.plasiyer = plasiyerid;
    ViewBag.cariid = id;
    ViewBag.fisid = kimlik;
    List<SelectListItem> grup = (from x in db.WEBSTOK
                                group x by x.GRUP into g
                                select new SelectListItem
                                {
 
                                    Text = g.Key,
                                    Value = g.Key.ToString()
                                }).ToList();
    ViewBag.grup = grup;
    var stok = db.WEBSTOK.Where(x => x.FIRMA == ad & x.PLASIYER == plasiyerid).ToList();
    return View(stok);
}