Move your hand to the outside, so your pinky is around the
locking collar, which is on the inboard side. Then rock your
hand counterclockwise, pressing down on the grip with the knuckle
of your index finger to hold the throttle still. Then hold
the collar between pinky and thumb, and flick it into the engaged
position by rotating it in the throttle-on direction. The collar
will spring into the grip when it is rotated far enough.