If a customer requires a refund, you will need to manage this via Catch.
The process is outlined in this FAQ: How to issue a refund
Once you have refunded the order in your Catch account go into Catchfeeder, go to Orders->All Orders from the left navigation and search for the order by Catch order number.
Click into the order by hitting the order number or view and then hit the "mark as refunded" button on the top right. This will not refund the order again, but it will update the status in Catchfeeder. You may also need to manually handle the order in your website as well.