I used to think calling customer service was the only way, but I learned the hard way after waiting on hold for an hour during a snowstorm! I found out the best way to manage a schedule swap is definitely through the "Find Your Trip" tool on their site.
Last week, I had to modify my flight to Dallas because of a work meeting. I just pulled up my reservation using my record locator, clicked "Change Trip," and followed the prompts to pick a new time. It’s super intuitive and saved my sanity.