Upvote:8
AirAsia has a "Manage my booking" option on their website. I don't have an active booking with them so I can't tell if you can adjust this detail, but the website does say you can "update traveller details".
If that fails, you'll need to call their call center. Last time I had to do that, it took quite some time to get through so it is a good idea to call right as the call center opens for the day (I mean literally to the second, as they open) if you can manage it.