If you want to give a customer credit your store you can issue them a gift card manually. To do this make sure you have first created a gift card.
Step 1: Navigate to your Product tab
Step 2: Select Send on your Gift Card
Choose the gift card that you want to send to your customer and select 'send'.
Step 3: Customize the gift card
Here you can enter in your customer's email, how much money you want on the gift card and how long they have to claim the card. You can also include a custom message that will show up in their notification. As soon as you select 'Send Card' an email will be sent to your customer.