Refunds are processed by Fiscal Host administrators. If you are not the admin, contact your fiscal host (or Donate PR support if your host is managed by Donate PR).
To refund a donation as a Fiscal Host admin:
Go to the Project page and head to the Budget section.
Click on View all transactions.
Find the transaction you want to refund on the list.
Click on View details. You will find a refund button right next to the transaction details.