1.First of all Install TWRP and download SuperSu file.
2.Download and install LG V10 USB drivers.
3.Now copy the Supersu file from your PC to your phone SD card.
4.Now turn off your phone and boot into recovery mode, press volume down and power key together.
5.Now select recovery mode, then tap to install and select the SuperSu file from you SD card.
6.Then swipe to confirm flash, then wait to comlete the process.
7.Now tap on reboot , it will reboot your system