The ability to return eBooks, eAudio, or eVideo early is dependent upon the platform.  All eMaterials expire automatically so technically it is not necessary to return them early.

Overdrive 

• Handheld Device: Tap the bookcover and hold. The option to return will appear if the publisher allows.
• Computer: Overdrive's instructions

Hoopla

• Click the return now button located at the bottom of the title on the title information page.