* First of all turn off your phone.
* Press Power + Volume Down button at the same time for some seconds.
* When the LG Logo appears then quickly release the Power button for a second and again press and hold the Power button
* Release the Button when the Factory Hard Reset menu will appear.
* Now press the Power button to begin and again press it to Confirm. Now your LG G4 will factory reset and the phone will automatically restart.
You have done all the process successfully
For more hacks check [https://guideusermanual.com/product-name-lg-g4-manual&po=325291&lang=English|LG G4 Manual.]