The American carrier typically doesn't charge customers to change their flights. Customers are just required to pay the fare difference. Think about the following circumstances:

whenever your new reservation is more expensive than your previous one.
If your new ticket is less expensive than the one you already purchased, Southwest Airlines will credit the refund amount back to the original method of payment.

Rules for Same-Day Flight Changes with Southwest Airlines

Southwest Airlines does not hesitate to accommodate changes to reservations made on the day of booking. When modifying a flight on the same day, there is no fee. They can make crucial adjustments to the reservation using both online and offline techniques.

whenever your new reservation is more expensive than your previous one.

If your new ticket is less expensive than the one you already purchased, Southwest Airlines will credit the refund amount back to the original method of payment.

Rules for Same-Day Flight Changes with Southwest Airlines

Southwest Airlines does not hesitate to accommodate changes to reservations made on the day of booking. When modifying a flight on the same day, there is no fee. They can make crucial adjustments to the reservation using both online and offline techniques.