To add a device to your profile, open the Scribble Scrubbie Pets app on the device you wanted added and login to your profile using your login credentials. If you have five devices already logged in, you'll need to remove a device before you can login with your new device.
To remove a device from your Profile, login to your profile using your login credentials and go to the Profiles section within the app then tap the "X" next to the device you want to be removed from your Profile.