Its the knob that you turn to turn the gas off or on or to reserve. There is a plug/cover in the middle of it covering up a countersunk phillips screw.
you pick the plug out
Take the screw out there will be a washer also
then you should be able to pull the knob off
unscrew the plastic hex nut
which should allow you to get the fuel valve plate off
behind it you will find the fuel valve.