There's an adjuster collar just under the top triple tree. Procedure is to prop up front of bike, loosen the top cap nut, loosen pinch bolt, losen upper fork clamp bolts, raise the upper tree slightly, adjust the collar, and then reverse the procedure to tighten everything up.
Collar accepts the same tool as the rear shock adjuster. Tighten it so that the wheel will tend to stay straight ahead but will still fall smoothly to the stop on either side if nudged slightly.
While the front end is up in the air, try to push the front wheel forward and back, side to side, to see if there's any play in the steering head. If you can't tighten up the bearings satisfactorily, or if it feels rough or "notchy", replace the bearings with a tapered bearing upgrade kit from All Balls.
mystic_1