How to make page appear only once

I have a project in Ionic 4 and create a new page in the app, but I need this page to appear only once when I open the app. I don’t know how to do this, I believe it has something like setRoot or rootPage as it was in the old versions, but I don’t know how to do it with the new Ionic 4 route system

What does “only once” mean here?

I believe only once means smthg like a login page that only appears once when users install the app. After seeing the page, it will never appear again.