How to find orders missing from order history?

Orders may be linked to an account using the order linking tool. When you log in, go to 'my orders' and scroll all the way to the bottom of the orders. There you should see a button that says "Are some of your orders missing? Find Orders". Once you click on that it will ask for the email address used on the order in question. Enter the email used on that missing order and then hit submit. You will be sent an email with a verification link that you must click on. Once you do the order should become linked to your account.