If you idle a 2 stroke too long you will foul plugs.. Why on earth someone would want to idle a 2 stroke is beyond me.
When I stop long enough to need to idle, I just kill it and restart. If the bike is right, it shouldn't take more than 2 kicks to get it started.
Anyway, on a 97 CR125 the idle screw is on the "choke" knob. twist it counter clockwise to increase the idle speed.
Ideally you should have just a few seconds of idle time, more than this and your throttle response won't be as crisp and you will tend to foul plugs quicker.