If the participant has paid ONLINE via credit card and you want to issue a refund for them, here are the steps:
1. Go to Registration and Registrations
2. Under the Participants tab, click 'Participants'
3. Click on the Registered Participant's name
4. Scroll down to the Payments & Refunds section and Click 'Online Refund'
5. Enter a comment and click 'Initiate'
Once the refund is issued, it should also appear as refunded in your league's Stripe account.