Broken seat adjuster

My passenger side seats back adjuster is split and no longer works, which is a pain because my wife likes to sit much more laid back than me.

I've bought a replacement.

Had a look at it over the weekend and can't work out how to swap them over? The screw in the middle just adjusts the seat…

How do I do it? Any help/advice appreciated!

Remove the screw?

I think there is 2 types, 1 type has a metal star type set up on it and the other is screwed on the shaft.

I tried removing the screw, but as per original post, all it does is adjust the seat.

I turned it until the seat was fully extended and it didn't want to shift any further…

I'm assuming there is something obvious I'm missing…