The access permissions of the Nuki Fob can be managed in the user management in the Nuki app. Tap on the Smart Lock and open the settings of the lock. Then choose “Manage users”. There you find the already authorized users and can edit them. If you have a Nuki Bridge this works even from afar.
A Nuki Fob can only have one access permission to exactly one Smart Lock. If you pair your Fob with a new Smart Lock you can not lock the previous Smart Lock any longer, you can only lock the new one.