Audi 80 2.8 V6 Auto- Gearbox Oil

[Pistonfest]

After just checking the gearbox oil fluid level (as per the manual instructions), it seems to be a little low. It was re-filled at the last service (about 4.5K miles ago), but needs topping up. Is this something I can do myself- if so, can somebody tell me where the filler cap is located please (I can't find it anywhere, and it doesn't show you where it is in the manual).
Or is this a task that only an approved Audi mechanic can do at regular service intervals?