In most cases, it is possible to cancel and rebook your flight if it has been less than 24 hours since making your purchase. Here is how to change or cancel a flight in your Trips List:

1. On the app's Home screen, tap Trips.
2. On the Trips List screen, tap the card for the flight itinerary that you want to modify.
3. On the Trip Details Card, tap Manage booking.

If there is any problem changing or canceling your flight, you will want to contact Expedia Booking Support. Here is how to call them from the app:

1. On the app’s Home screen, tap Account.
2. In the Support section, tap Contact booking support.
3. Tap the phone number displayed to call the Booking Support team.