TROLLING VALVE

Hi all
I wonder if someone can tell me how to operate the trolling valve on my 215 I understand when to use it etc but do I unscrew the lock collar and pull out the plunger to the required speed? then push the red knob back in and retighten the collar,so frightened of damaging the gearbox.The boat is so difficult to get on my berth it goes to fast with poor steering,have to put it in and out of gear to manoeuvre around the gin palaces berthed close by.Thanks T.J.