Android app signing: for an existing app with “OPT OUT”, can I change it to [App signing by Google Play]

Question

1. As the title, we released an app but had selected the "OPT OUT" as the attached screenshot. Can we change it to [App signing by Google Play] as like clicking the [Continue] button? Because this app was released for a year, and got some users, we do not want to create another app to replace it and restart again.

2. It looks like we should go to [App signing] of the existing app to do the option [You've exported your app signing key](as the screenshot below). But when uploading the key store file used in Android Studio [Generate Signed APK], it appears error. In fact, we do not exactly understand the logic of key files. Any idea or experience is welcome.

Answer 1

Yes, as long as you still have a hold of your keystore (if you already have published an APK).

You need to upload an APK first, then go to the "App Signing" menu on the left-hand side bar and follow the instructions, and you will be able to enroll in App Signing by Play there.

Alternatively, delete the app and recreate it. Faster, but not always an option :)