To return an ebook from your Kindle:
On your computer, go to www.amazon.com/manageyourkindle and log in to your Amazon account.
Once logged in you will see a list of all of your Kindle content.
Find the library book by title in the list and hover your mouse pointer over the ACTIONS button out to the right side.
In the menu that pops up click on RETURN and then confirm the return
The book is now off your OverDrive Digital Library account.