Originally Posted by Adam Smith

Go to the customer service webpage. Go to the dropdown under "How can we help you?" Select "Comments / Issues / Suggestions". Hit "Send us an email". There will be an option for "Refund Request", and when it gives you the dropdown for what type of refund, select seat fee or preferred seat fee (as applicable), then fill out the forms.

You may want to find the ticket number in the original confirmation e-mail, but the PNR may be sufficient; I'm not entirely sure.