If instead of a refund, a patron offers or requests to turn their payment into a donation, you can transfer the value of their ticket into a donation for them.
How to transfer the funds from a ticket purchase into a donation:
Look up the patron's record on the DATABASE screen, locate their order at bottom left and process a refund*, select Donation as the Refund Method on the second screen in the process(do not refund it to their CC). It will create the refund on the current order and create a new donation order for the refund amount. Check the "do not send email" checkbox if you don't want the patron to receive a refund email. Note that the patron will still receive a donation acknowledgment email.