Hi i have a 97 a4 1.9 tdi se the headunit has gone into safe mode after the battery died audi wany 100 quid to re input code i have removed and there is a code on the top of the unit but i have no idea how to enter is there a sequence of buttons to press etc iam prettycompetent at car electrics and other mechanics but the car came without any instruction manual

any help would be appreciated