Typically, one pops the current page using this from the NavigationStack:
Navigation.PopAsync( true );
How to I use Naviga
I'm assuming that the data model that you are using is not observable/bindable and thus the page is not "auto-updated"...
You could use MessagingCenter to publish a "Refresh Event" to avoid coupling the two Pages with events...
In your MainPage:
MessagingCenter.Subscribe (this, "RefreshMainPage", (sender) => {
// Call your main page refresh method
});
In your Second Page:
MessagingCenter.Send (this, "RefreshMainPage");
Navigation.PopAsync( true );
https://developer.xamarin.com/guides/xamarin-forms/messaging-center/