Prerequisites:

1. LG Drivers
2. SmartFlash Tool
I have recently had an LG p970h phone which I wanted to do a full reset since I did not have the unlock code.
Since pressing the down button along with the power button did not bring up the recovery options I had no way to do a hard reset with the buttons themselves and therefor had to use a computer.
These are the steps that helped for me:

1. Install the LG drivers
2. Extract the smart flash tool to a folder on the desktop
3. Shut off the phone
4. While holding the up volume plug the phone into the computer
5. Wait for the drivers to install
6. Run B_SmartFlashTool_Extern from the smartflash tool folder on the desktop folder
7. On the first tab called Normal D/L select erase user data and click start
8. Wait for the phone to restart and you are done