You Can Use The Below Method For Upgrade LG G3 D855P/ And If You Want To Hard Reset It By Flashing The Stock Rom/ In Case If You Are Using Any Custom Rom And Want Back To Stock Rom And Official Firmware Or Facing The Boot loop Problem. This Method Is Also Useful For Sudden Death/Bricked/Not Power And Also After Flashing The Stock Rom imei Null or Unknown Base band Problems Can Be Solve.
How To Unbrick LG G3 D855P Stock Rom With Kdz :-
1. Extract the file “LG Flash Tool 2014.zip” and run the file “LG Flash Tool 2014.exe” as administrator.
2. turn on Download Mode . Turn off your phone. Hold “Volume +” and connect to the PC via USB Or Hold “Volume + and Volume – at the same time.
3 Your window have to be like this.
After making the settings shown above, press the folder icon with an arrow and select your downloaded .kdz
5.Now click “CSE Flash”
6 . Press “START” in the window displayed.
7. Let the new window “Select Country & Language” that way and click “OK”
Wait until 100% to complete !