Press and hold the Power button
Tap Restart or Reboot
If Restart is not available, tap Power off
Wait for the phone to turn off completely
Press and hold the Power button again to turn it back on
If the phone is frozen, press and hold Power and Volume Down together for 10 to 20 seconds
Release the buttons when the screen turns off and the phone restarts
If needed, charge the phone for a few minutes and try again