Ok, they should have really labelled this or put a note somewhere.
You use your old backup (which I didn't know about) - which can be found by pressing 'Backups' on the menu screen after accessing the application. It's the first backup on the list that would be the one with your old firmware (before it was spoofed).
They should have just made a "activate - deactivate" button instead of hiding it and not releasing any notes or instructions. It was pretty confusing.