Refunds work the exact same way as any other card purchase.
First step is to contact the Retailer that provided you the products to arrange the return and ensure the products are sent back in a saleable condition.
Once the return has been accepted and a refund has been processed by the Retailer you have purchased from, any outstanding payments will be cancelled and any funds paid will be refunded back to you. This is dependent on the amount refunded against the order by the Retailer.