I accidentally refunded the wrong person or wrong amount. What can I do to fix it?
When you first generate a refund, it has a status of Pending and remains in that status for up to two hours. You can cancel an incorrect refund while it is in Pending status by clicking "Cancel all pending refunds for this order."
If you do not see this "Cancel" link, the refund has been released to the buyer and cannot be cancelled. In that case, you can inform the buyer about the incorrect refund and ask them to contact Amazon Customer Service to request a recharge on their credit card