Sleeve 1021 for the steering tube, in which the extendable handlebar moves back and forth.
You can easily replace the steering sleeve. Unscrew the screw on the back of the handlebar clamp, push the clamp up and pull out the top part of the bar. You can now look into the bottom of the steering tube from below. Sometimes the sleeve is still in it and it has been pushed down into the rod. If it's gone, you can put in a new one and put the steer back together back in reverse order. Make sure the clamp is adjusted tight enough to allow the handlebars to remain at any height.