You can change from app as well
From the AS app, click on the three dots next to your itinerary banner. Option for change should appear. Follow the link and select the best option.
For me, i decided to change to alternate airport. I was originally booked from JFK but looked at LGA and EWR. Some option even entirely on AA were some alternative with free change option. I decided on EWR nonstop option however.
Jiburi