Join Date: Sep 2007
Location: Basingstoke, UK
Programs: Virgin Flying Club Silver, Executive Club Blue, Miles & More, Priority Club Gold, Skywards Blue
Posts: 464
MMB = Manage My Booking
It's on the BA website.
You will need to enter your booking reference and your surname, then you will have access to all details of your booking and you just need to follow the processus mentioned above.
Hope it helps.
Julmops.