dunno if mfa display/mileage the same as on mk4 but i kno whow to clear all mk4 service codes!!,
put key in ignt (not turned on yet) hold down reset button near (mileage clock) for about 6 seconds, turn on ignition then you should get '-----' or similar then turn your clock reset button either left or right to eliminate this then display back to normal!!, welll this is fo rmk4s so no promises it will work on a mk3!!!