If you need to cancel a sale for any reason, it’s a quick fix.
Go to Studio for desktop > Sales History and check the box next to the item, then
click Cancel Sale. You will be asked to confirm – cancellation cannot be undone!
Click Confirm and your item will be added to your available quantity.

Tip: If you cancel a sale by mistake, all you need to do is find the item in your available inventory and mark it as sold again. You will need to fill out the sale information again.