This will depend on how you used your gift card:
Did you pay for your order in full using a gift card?
In this case, it will be added back to your gift card total on your Khan account. You can use it for your next order against eligible items. You can check your current available amount at any time under “Gift cards”.
Did you pay for your order by combining a gift card with a different payment method?
The gift card is valid for fashion items. When you return one or more of these items, you will be refunded to the other payment method selected at checkout when you placed the order. For example, if you used a credit card as well as a gift card, you will be refunded to your credit card and the gift card will be applied to the kept fashion items.
Did you pay for your order via invoice and gift card ?
If you used your gift card for valid fashion items against part of your order, and selected invoice payment for the remaining amount, and you return an item, the open amount on the invoice will be reduced
If the gift card amount is larger than the open amount on your invoice, you will be refunded to your gift card total.