Return Requests that have items marked as Received will be visible in Orders>Returns in the Returned filter.
If you are have permission to process a refund payment and mark the Request as paid follow This Guide. Otherwise change the status of the Request to Ready To Refund and hit Save. The relevant person will then be able to view this request and process the refund.
If items were Received back to the warehouse but the customer would like them to be resent then follow the steps in This Guide. Once you have re-shipped the order add in a note in the Request and mark the status as Completed then hit Save.