Doubt changing window-based app in navigation-based app

Hi, I was trying to create a navigation-based app starting from a simple window-based app.
I noticed that if I create a new project as "Navigation-based application", XCode creates a default project in which the navigation controller loads the view from "RootViewController".

How can I obtain the same effect in my window-based application?
I mean, I achieved to transform my wb application in a nb one, but the view loaded is "MainWindow.xib". This is my navigationController:

I want it to load the view from another view controller (or another xib).

What I do not get is how can XCode tell to the navigation controller to load another view without saying explicitly in the code (or, at least, I did not find the point in which it does)...