Two step verification is the process that occurs when pairing the Fender MUSTANG GT with a mobile device for the very first time. A message asking if the displayed information on your device matches the displayed information on your Amp.
After pairing, you can forget your Mustang GT in the Bluetooth list on your mobile device but the amp will still try to pair the next time you power-up. Just press CANCEL on the mobile device or NO on the amp when you get the pairing message. Next time you power-up the amp will not try to pair with your mobile device.