I believe that you want to open a different dialog box.
I organize my WPF controls like so, in a form of the MVC pattern:
views <==> controller <==> data
So, when you click on a view, the controller handles the logic of the click, kind of like how a web server handles the logic of user input. The controller then determines whether to open another view or not. If the user input requires some storage or handling of state, then the controller passes that off to the 'data' section. That data class will then put things to disk, if necessary. The controller could also pass off to a 'processing' class, that will process the input and give it back to the controller, which then determines whether to display the results to the user, put them in a file, both, or neither.
tl;dr- put your control logic in a backend class rather than the window itself. That backend will then open another window.