I will describe a few simple steps to perform a hard reset on the Lenovo S880:
1) Turn off the device if it is on.
2) Press the volume up button and the power button at the same time, wait for the “Factory Mode” menu to appear.
3) In the menu, press the volume button up to highlight the item “Clear eMMC” and select it by pressing the volume button down.
4) When the cleaning is completed, select the “Reboot” item in the menu, after which the device will reboot.
Done!