Across the top, you will see several yellow tabs, click the one labeled "My HC". 

On the left side of the page, you will see a light yellow box; click the second item down labeled "Purchases". 

You will then see a box, listing all of your recent purchases.  On the right hand side of the box, you will see a column labeled "Feedback". 

Find your DeeLee Slings purchase, and from the row click "Leave Feedback". 

A feedback form will pop-up in a new window, and from there you can leave feedback!