If you are using Adobe Digital Editions…
Open Adobe Digital Editions.
Select the 'Library View' icon (in the upper left corner).
The Adobe Digital Editions library is displayed.
Under the 'Bookshelves' heading, select 'Borrowed'.
Click the eBook you want to return.
Click the 'Item Options' arrow (in the upper left corner of the selected eBook).
Select 'Return Borrowed Item'.
Click 'Return' to verify that you want to return the title.
The eBook is removed from your account and returned to the library collection.
Amazing what you can find it you just look. Thanks, epiphany!