How do you set face unlock on LG G3 after update to Android Marshmallow ?

[AC Question]

How do you set face unlock on LG G3 after update to Android Marshmallow ?

I have upgraded LG G3 to Android Marshmallow and cannot seem to find how to get face unlock to work.

I have set trusted face but cannot see how to enable face unlock to work.

All help appreciated.

Thank you.