You can refund a participant (and revoke their access to the course at the same time) via the manage → participant list page.
Refunding Stripe Payments
For Stripe payments there's nothing you need to do - it just works!
Refunding PayPal Payments
PayPal requires an extra step. After connecting your PayPal account you'll see a button to grant refund permissions to CourseCraft:
Click that button and you'll be taken to this page on PayPal:
Click Grant Permission and you're done!
Note: PayPal only allows refunds for 60 days. The refund button will not be available if the participant has been enrolled for too long.