In your case, you will have to reset the phone, which will erase everything on it including the pin.
- Turn the phone off.
- Press and hold the following keys down: Volume Down and the Power button
- Let go of the power button when the LG logo shows and immediately press and hold the power button again. (this whole time, you are not letting go of the volume down key)
- When the factory hard reset screen appears, let go of all the buttons.
- Press the Power button to continue. If you press any of the Volume keys, it will cancel.
- Press the Power button again to confirm the reset.
Once that is complete, you will be all set.
Please, let me know the results of this once you are done.