If he purchased a Anytime Ticket or Business Select he could request a refund. See below.
Modifying a refundable fare will result in the fare becoming NON-refundable. To ensure your new ticket is refundable, cancel your existing reservation, request a refund of the refundable balance, and create a new reservation. Non-refundable fares may be applied toward future travel on Southwest Airlines for the originally ticketed Passenger only.
Upgrading to Business Select will result in your fare becoming NON-refundable.
Just want to add that your brother can use the travel funds from the refund (assuming you purchased a non refundable Wanna Get Away fare) within a year from the original purchase date. Travel must be completed within the year.