1. Look under the head of the bolt and you will see a straight metal edge (red arrow).

2. On the clamp you will see a notch cut out on the clamp (blue arrow).  

3. Insert bolt into clamp from the seat side of the frame.

4. Next slide the washer on the bolt from the outside of the frame.

5. Now attach the knob to the end of the bolt. Adjust armrest to the height required and

    tighten knob.