Admin Mode is a view in the kid's app where the parent can access by entering a passcode and remove the restrictions and unlink the device, for the case when there's no internet connection or the kid's device is orphaned.
To access the Admin Mode you need to set the passcode first. Tap the settings icon at the top right corner of the main view(Or break screen) of the kid's app, Then tap "Set passcode". If you already have set the passcode, you won't see the option.
Once you set the passcode, you will see the "Admin Mode" option in the same menu. Tap the option, and enter the passcode you set before. Then you will enter the Admin Mode.
From the Admin Mode, you can pause the restrictions, unlink the device, and change the passcode in case the kid figures out the passcode. Please don't let the kid know the passcode.