If you need to refund and order. Locate the order in the incoming or recent tabs on the orders screen and press "reject" or "cancel order". The customer immediately receives a text message letting them know their order has been turned down. If you need to contact the customer to discuss the order, their contact information is displayed on the ticket. You can also send them a text message from the inbox.
All charges are automatically refunded when an order is canceled or rejected. The customer is also made aware of this via a text message. You can find the order (and refund) within your Square account transaction history.