Navigation.InsertPageBefore(new MainPage(), new NavigationPage(new
  PeppyMasterDetail()));
            await Navigation.PopAsync();

if (!string.IsNullOrWhiteSpace(Settings.AccessToken))
           {
               MainPage = new NavigationPage(new PeppyMasterDetail())
               {

               };
           }

           else if (string.IsNullOrWhiteSpace(Settings.UserName) && string.IsNullOrWhiteSpace(Settings.Password))
           {
               MainPage = new NavigationPage(new MainPage())
               {
                   BarBackgroundColor = Color.Purple,
                   BarTextColor = Color.White
               };

           }