Custom PowerApps Form on SharePoint list with existing PowerApp

I'd like to know if it is at all possible to set an existing PowerApp as the custom form for a list. I don't see how to set the Custom Form setting in the list through GUI or PowerShell to an previously existing PowerApp.

 

Or what would be your method to use an existing PowerApp as a custom form for a list? Is there a way to easily copy a PowerApp into the one that is created when you click customize forms in the SP list? 

 

I want to achieve to have a single PowerApp that is available in the PA Mobile App and in SharePoint on the list. The PA I already have has multiple screens and uses multiple lists.