British Airways Change Booking Guide : If you need to change your flight, seat or baggage allowance, or meal preference, then please contact us. To change your booking Visit the British Airways website and click “Manage My Booking” at the top of any page. Select your journey from the drop-down menu that appears under “Bookings” and click “Change Flight/Seat/Baggage Allowance/Meals”. If prompted for a passenger name and booking reference number (PNR), enter this information in their respective boxes on this screen. Then select whether you want to cancel or reschedule your trip and follow through from there to complete your changes. Alternatively, if you have already created an account with us but cannot find it on our website when trying to make changes on our site then please call us so we can help!

https://www.skytripaway.com/flights/fly-british-airways-ba