When is a customer refunded after I cancel an unfulfilled order?

[wonena-dev]

Hi! I just launched my website. I sold an item that I 've run out of stock. I canceled the order, but the system sent The following notification

Your order has been canceled

Order #1006 was canceled because we did not have enough stock to fulfill your order and your payment has not yet been refunded.

Then I went back to the order, but it doesnt' have any option to refund. How do we do this?