How to dismiss modal navigation page using Prism NavigationService?

In my root view model I call something like

await _navigationService.NavigateAsync(
    "/NavigationPage/Page1of2",
    useModalNavigation: true
);

Sure enough it loads both view models in a modal navigation just fine. In Page1of2ViewModel I do another

await _navigationService.NavigateAsync(
    "Page2of2",
    useModalNavigation: false
);

Which view model now should dismiss that modal and how?

Using GoBackAsync() or GoBackAsync(useModalNavigation: true) neither of the 3 view model seem to be able to dismiss the modal flow back to my root view model.