Head to the Gift Card area
Hover over the 'Products' menu and select 'All Products'
From the 'Products' page, find your product, click the more button and select 'View Giftcards'
Find your Gift Card
You will be taken to the Manage section of your Gift Card product. Type in the gift card ID into the search box that appears, this will show the exact gift card you want to edit
Click the more icon for that row and select View giftcard
Find the Booking ID
On the Gift Card details page, click the link for the Booking ID
Cancel the booking
The gift card is linked to its booking ID, if you cancel the booking ID, it will automatically cancel the gift card in effect. On the Booking page, click the 'More' button and select 'Cancel booking'. pop up modal will ask you to confirm - please note, this action is not reversible