The photos below will help you identify
which version of adjustment mechanisms
your chair has!

There are 2 cover attachment bolts (red) in the middle of the back cover, with the width adjustment screws right next to them (green)

The cover attachment bolts have moved to the outside edges, and there are now 4 of them total.

there are also no width adjustment set screws on the sides of the cover

The video below shows the procedure for adjusting both styles

(use the time codes to skip to the appropriate part of the video :^)

(click the youtube logo at the bottom of player to open in a new window)