How to achieve app.current.mainpage= new navigationpage(new somepage) in prism

I have n number of page in my application after some functionality i have to make one page as main page (app.currrent.mainpage =new navigationpage(new somepage);). how to achieve this in prism.

Nuget Library : Plug.forms 7.0.0.336-Pre

I'm using prims. this problem is facing only in android device
I have tried below in my code :
1. await _navigationService.NavigateAsync("myapp:///NavigationPage/MainPage") - Relaunching the application.
2. await _navigationService.NavigateAsync("Main/Navigation"); - Navigating back to old page that is on the stack.

Let me know am I missing something.