Escrow cannot be refunded until the Escrow Receipt is posted in full to an Encounter. You can use any recent Encounter to post the Receipt. After posting the Receipt, the Refund can be done using the Post Refund button on the Payments Dashboard or the Post Refund link from the Patient or Encounter Dashboard.
If the Patient does not have any Encounters, you can create a zero dollar Charge, and post the Escrow Receipt to the Encounter that was created. There will be a negative balance which the Refund can be posted against leaving a zero balance.