Performing a factory reset using phone buttons
If you cannot turn on your phone or access the phone settings, you can still perform a factory reset by using buttons on the phone.
With your phone powered off, press and hold the VOLUME UP and VOLUME DOWN buttons.
While holding the volume buttons, press the END/POWER button briefly and then release it.
When you see a warning message on screen, release the VOLUME UP and VOLUME DOWN buttons.
Press the VOLUME UP button to perform the reset, or press any other button to cancel the reset.