How to cancel a flight on American
Step 1: Sign in to your account on the American home page and select Your Trips
Step 2: Once you have selected the trip you want to cancel, select Cancel Reservation.
Step 3: The next screen will ask you to confirm that you want to cancel your reservation.
Step 4: After clicking confirm, your reservation will be officially canceled and you will receive a coupon for the remaining funds after possible cancellation fees.
Step 5: The last step is that you will receive the confirmation message in your registered email with your refund code and a ticket number.
American Airlines Flight Cancellation Policy If you cancel American Airlines in accordance with its terms and conditions, you can request a full refund on your booked American flight.

Can I cancel an American flight within 24 hours?
Yes, all customers will have 24 hours from the time of their original reservation to cancel their reservation without being charged a cancellation fee, regardless of the rate selected.
If you purchase a refundable ticket, you are eligible to cancel your flight for a full refund by requesting a refund online or by contacting the reservations department.
If you purchase a non-refundable ticket, you are not eligible for a refund after the 24-hour grace period.
However, if you cancel a flight prior to departure, you can apply the unused value of eligible fares for future travel, as long as the new flight takes place within one year of the original ticket issue date.
https://www.customerhelplinenow.com/american-airlines-cancellation-and-refund-policy/