How can I rebind the drowdownlist in edit page MVC?

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C#

MVC

I am working on MVC 5, there I have Viewmodel Class ' PartnersVM '.

public class PartnersVM  
   {  
       public List<CountryVM> listCountry { get; set; }  
       public PartnerVM listPartnerVM { get; set; }  
   }   
  
public class CountryVM  
   {  
       public int idCountry { get; set; }  
       public string countries_name { get; set; }  
   }  
  
public class PartnerVM  
   {  
     public string ServiceDistricts { get; set; }  
     public string ServiceStates { get; set; }  
    }  

What I have tried:

And this is ActionResult Get method.

[HttpGet]  
public ActionResult PremiumUserRegistration()  
       {  
         PartnersVM objcountrymodel = new PartnersVM();  
          objcountrymodel.listCountry = new List<CountryVM>();  
                       objcountrymodel.listCountry = objPartnerBIL.ShowCountries().Select(item => new CountryVM  
                       {  
                           idCountry = item.idCountry,  
                           countries_name = item.countries_name  
                       }).ToList();  
return View("PremiumUserRegistration", objcountrymodel);                      
        }  

After calling this actionresult now binding list of countries. And the dropdown onchage calling a jscript function for bind below dropdowns also.

View:

@Html.DropDownListFor(model => model.listCountry, new SelectList(Model.listCountry, "idCountry", "countries_name"), "Select", new { @class = "form-control ", @id = "ddlcountries", @onchange = "return getuserstate.search(this.value)" })  
  
  
@Html.DropDownListFor(model => model.listPartnerVM.ServiceStates, Enumerable.Empty<SelectListItem>(), "Select Country", new { @id = "ddlstate", @class = "form-control ", @onchange = "return getdistricts.search(this.value)" })  
  
  
@Html.DropDownListFor(model => model.listPartnerVM.ServiceDistricts, Enumerable.Empty<SelectListItem>(), "Select State", new { @id = "ddlDistrict", @class = "form-control " })

Here getting those drowdown's value while going to edit Get action method as show below image.

[^]

Now, all are working fine. But the problem is, I can not rebind those drowdown list while moving on edit page. Here Add/Edit page is one. How can I rebind the dropdownlist?

Please help me...