Booting into recovery on the LG G6 isn't as straight forward as other devices. The stock recovery mode also doesn't have much to offer. All you can do from recovery is perform a factory reset (which can be done without recovery).
How to boot into recovery:
- Power off the phone
- Hold the Volume Down
- While still holding Volume Down, hold the Power button
- Hold both until the LG logo appears
- When the logo appears, let go of only Power for a brief second
- Continue holding both until Recovery appears