Here are the instuctions I found
Directions - Please read them carefully
Please make sure you have your LG Drivers installed before you start this process
you can go to Lg site to get current usb drivers
Please download one of these zip files from this links below
LS840ZVC https://www.dropbox.com/s/j63hoo0jsocid8y/LGVIPER.zip
LS840ZVD https://www.dropbox.com/s/3timbamztkewkdh/LS840ZVD.zip
Unzip and place the LG folder in C: root directory
Please have at least 60 percent battery or more and put the phone in download mode.
You can do that by Plugging the usb cord while hold vol up and power. Keep holding it until you see a screen that says downloading in progress.
Now go to your device manager and look for your com ports and find your LGE Android USB Serial Port.(not modems) Now double click it and look for advance and then click it. now we have too change the com port to 41. press ok and close it out.
Unplug your usb connection from phone and leave phone in download mode.
Now open your windows explorer go to C:\LG\LGFLASHTOOL\LGFlashTool.exe run as admin.
Model config will open select manual mode assign LS840...dll for dll and .tot for s/w.
Go to port settings and select port 1 only.
Now plug your usb cable back into the phone.
start the flash by pressing the arrow on the top left side and let it run
--> !! Please don't let your desktop or laptop cutoff during the process. Please do not remove phone from usb cable until after the first reboot complete.
It doesn't matter what percent your LG FlashTool is showing and you can close out LG FlashTool at that point. do a factory reset after you get too your home screen for the first time. now you device is ready too be used.
don't forget to update profile on phone after it reloads
Source