Processing a refund with Square is completed in both apps. Let's get the customer sorted first.
In Square:
Pop into the Square app on your iPad
Follow their process to perform the refund (hot tip: head to transactions, locate it and press refund)
In Bustle
Head to Settings > History in the Bustle till app and press Transactions.
Locate your transaction and press it to select.
Press the Refund button.
Select a refund reason or type in a different reason and press confirm.
Select the items you wish to refund and then do a LONG press on the Card button. This bypasses Square (which is already done) and records the refund in Bustle