First, you'll need to go to your product listings page. To do this, go to your seller Dashboard. In the navigational menu on your Dashboard, hover over products. Choose the drop-down option product listing - this will bring you to your products page. Click on the blue button ADD PRODUCT near the top of the page.
To add a product as a link, you will want to ensure that the choose product option, located on the top left hand side, is set to digital. Then, scroll down to digital product details, located on the right hand side. Choose from the add digital product as drop down digital product as link option.