Google Analytics for an other instance of firebase project

I am developing two apps connected to the same Firebase Authentication and Real Time Database.
The first one consumes data for users, the second one is a backoffice app for enterprises to edit data users of the first can view.
I would track analytics on the both app, but my goals are different, so I would like to have 2 Google analytics properties. But for now, my 2 apps are on the same firebase project, so in Google analytics I have 1 property for my 2 apps, and I can’t track easily my goals.

How can I configure the firebaseConfig I give to the firebase.initializeApp method, or my google-services.json (and info.plist) files to access the already configured database, but track my analytics in an other firebase project ?