American Airlines doesn't allow flight changes to Basic Economy tickets on homegrown flights, i.e., trips inside the United States, just as trips to/from Canada, the Caribbean, and Central America. Be that as it may, it permits flight changes on worldwide trips between the United States and Europe for a change charge of up to USD 750.

American Airlines Change Flight

https://manageairlinesbooking.com/blog/can-i-change-my-flight-date-on-american-airlines/