Go to Inspections -- View Inspections -- Actions -- Payment Information (or click the $ icon if you're using icons) to look at payments on your order.

If the credit card payment was taken directly through ISN click on the little blue  refund link next to the payment near the top:

If you just want to issue a partial refund you can change the amount in the text field for refund amount, otherwise click the link to issue a full refund amount for what was charged to the card.

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