programming key to a4 b7

[wrx fifer]

just bought an audi a4 b7 private sale with one key fob, had no battery in it, so bought new battery and the led flashes on the key now but no matter what i try cant seem to get it to work opening and locking the car, i have to put in door to open car, only got the one key fob but also got the plastic master key with the stuff i got with it.

have tried numerous guides found online but nothing seems to work can anyone on here that knows audi help at all?

Grant