Dropdownlist asp.net mvc

I have a product that can be registered in 2 stores A and B if I have already made a registration in A how do I pro Dropdownlist show me only show option B the next time I register? How would logic be? using Entityframework and Linq?

[HttpGet]
public IActionResult Create(string businessId)
{
        var marketRest = new Rest
                             .MarketplaceRest(_appSettings.WebApiUrl, _appKeyBase64);

        var registerViewModel = new RegisterMarketPlaceViewModel
        {
            BusinessId = businessId,

        };
        registerViewModel.MarketNameSelectList = 
                registerViewModel.GetMarketplaceSelectList(marketRest, _memoryCache);

        return View(registerViewModel);
}