How do you reset the stereo system when it reads SAFE?
Owner's manual. Don't have one, get one.
Apart from having the owners manual, which expains the proceedure, you also need the code - Originally supplied with the car paperwork concerning the radio. Finally an Audi dealer can link it all to to their computer and find out the details, but you'll need the Registration V5 Form and a driving Licence or passport with your photo.