Developers at XDA forum have shared the flash tool and stock firmware files for LG G3, using which users can restore stock firmware on their devices.
Those who have accidentally bricked their devices and want to unbrick or unroot it and reinstall stock firmware can do so using the firmware files available at XDA. Unrooting will reinstall all the factory and default restrictions on the Android device.
LG G3 users, who are currently looking for an unroot method, may follow our unroot guide below.
Do not forget to back up all data of the handset, before following the tutorial. Additionally, ensure that the device has above 80% of battery charge.
Steps to unroot LG G3
Step-1: Download Flash Tool and drivers for LG G3 from here. Save these files on the computer
Step-2: Install the drivers by following the on-screen instructions
Step-3: Unzip and set up LG flash tool zip on the desktop and then run the executable file and install the programme by following the on-screen instructions
Step-4: Right-click MegaLock.dll and copy it to C:> LG> Flashtool
Step-5: Place the LG G3 into download mode. For this first turn off the phone and connect it with computer while holding the Volume Up button
Step-6: From the computer launch Device Manager and right-click LGE Mobile USB Serial Port and select Properties then Port Settings>> Advanced>> change the COM Port Number to 41
Step-7: Download the stock Android firmware for LG G3 from here. Download the .bin and .dll files on the computer
Step-8: Open the Flashtool programme from the computer and select Manual Mode
Step-9: Load the .dll file by clicking the three dots option
Step-10: Click Add to the right of the S/W section and select the .tot file
Step-11: When it says Ready, unplug the LG G3 for a few seconds and plug it again. This should automatically begin the installation process
Step-12: Once the installation process is completed, the phone will reboot
Now you should be able to enjoy the stock firmware on the LG G3.
[Source: Android Geeks]