All eBooks expire on their own, so you do not need to return them early. They will disappear off your library account and device once they have expired.
If you want to return early, it depends on which format (i.e. ePub, kindle, OverDrive Read, Axis360 eBook, pdf), device (i.e. Android tablet/phone, iOS tablet/phone, personal computer/Mac, laptop, etc.), and eBook provider (i.e. Axis 360, OverDrive, etc.) you had checked out this digital title.
If you checked out your digital title from OverDrive and would like to return early, here is a link with more information:
If you had checked out your digital title from Axis 360, here's a link with more information on how to return early: