How do I reverse a accidental redeemed online gift card

Hope you can help. My auntie purchased a gift voucher as a gift for christmas. When clicked to redeem the gift card it said it had already been redeemed.

When I mentioned to my aunt, she said she accidently redeemed.

She has not spent on anything so wondered if there is a way of reversing.

If yes - can you go through what she needs to do?

If no - can you let me know what she should do with current redeems and how to action another voucher?

Thank you for your advance.

K

:)