I am not sure if you booked using an Advantage number. If you do, your secure flight info (name, gender, date of birth, etc) is part of the account and you can’t change it without a lot of effort.

If you view the reservation on the web site (aa.com) using your confirmation code, down at the bottom there is a link to add/edit passenger information, but I am not able to view date of birth anywhere that I can find.

In the app, “manage trip” will get you to a similar place with the add/edit passenger information link.

To verify date of birth you might have to call.