seems to work fine Since it's not built into your previous codebase, I can't think of an easy way to associate the GCM token with Firebase. However, GCM and FCM tokens both work to send to devices from the FCM endpoint. Assuming you're using the same project for GCM and Firebase, you can take advantage of this. When a user updates to the new version of your app that uses FCM, when the token refreshes, the previous GCM token will be invalidated. You could send a message to both GCM and FCM tokens. Since you get a response telling you if tokens are invalid, as the GCM tokens come back invalidated over time when users update, you could remove them from your database.
This might help you Since you already have data in your tables then instead of rollback your migrations (which will cause data losses) you can create new migration files to update your tables. Suppose you have a table users with columns name, email, password. You stored data in that table. Then you realized that you also do need to add a new column named mobile_no to your users table. To do this you need to create a new migration file. Command will be: