Yes—the number attached to your booking can be changed, although an existing BA number may be locked in the online form.

Try these options:

1. **Open [BA’s Manage My Booking](https://www.britishairways.com/travel/managebooking/public/en_gb)** using your booking reference and surname, while signed out of your BA account. Look for the frequent flyer details and select **American Airlines / AAdvantage** if editing is available. BA officially supports adding partner frequent flyer numbers, but doesn’t guarantee that an existing number can be replaced online. [BA’s FAQ](https://www.britishairways.com/travel/mmbfaqs/public/en_gb)

2. **Try Finnair’s “Manage booking” with the same reference and surname.** This is a reported workaround for changing frequent flyer details on other oneworld airlines’ bookings, even without a Finnair flight. It may not work for every reservation. [Workaround instructions](https://pointstobemade.com/how-to-alter-your-frequent-flyer-number-in-oneworld-bookings-as-many-times-as-you-want/)

3. **If the field remains locked, use [BA’s live chat](https://www.britishairways.com/content/information/help-and-contacts/contact-us)** and ask an agent to replace the BA number with your AAdvantage number **on every segment, including Iberia**. Travellers have reported successfully making this exact change through chat, avoiding a phone call. [Recent report](https://www.reddit.com/r/BritishAirways/comments/1rj9iqz/change_frequent_flyer_info_in_booking/)

Afterwards, reopen the booking and check that the AA number appears throughout the itinerary.