Cannot deploy rules to Firebase project with multiple databases

I'm getting the error "Multiple databases found in the Firebase project. Deploying rules to projects with multiple databases currently is not supported".

Please update your rules in Firebase manually: https://firebase.google.com/docs/rules/manage-deploy.

I have no idea how to set my database to default from Flutterflow, but I can see under Advanced Settings there is an option to select a 'default' and cloud function region dropdown.

If anyone has encountered this issue, p.s guide me how to address this problem.

Thanks,

Frederic