1. You must have ROM Manager installed and or ClockworkMod Recovery flashed and an external sdcard installed. Then have the directory and file contents of the "LG-P999-V10f.zip" or "LG-P999-V20e.zip" file extracted to your external SDCard in the /sdcard/clockworkmod/backup/LG-P999-V10f directory. If the directory does not exist then create it.
2. Run ROM Manager and choose Reboot into Recovery or boot phone into clockworkmod recovery.
- There must be a directory called "LG-P999-V10f" or "LG-P999-V21e" or "LG-P999-V21y" in the "/sdcard/clockworkmod/backup" subdirectory and the files must be directly in that directory, not in another nested directory or Nandroid will not find the files. (Note: If you have any spaces in your directory name. You will get a md5 check some error.)
3. In recovery go down to backup and restore, choose restore.
4. Select LG-P999-V10f or LG-P999-V21e or LG-P999-V21y and choose Yes - Restore.
5. When the restore finishes do not reboot yet. Do a "wipe data/factory reset" from the recovery menu (just to be thorough).
6. When it completes choose Reboot.