Hi, had this happen to me recently too, and found an easy way to get the cover off etc - and design that is not exactly true to the ‘Simply Clever’ slogan.
Firstly it’s far too easy for luggage to knock this cover up and out of position, with button stuck permanently up.
Three things happen inside:
1. the hook (A) that holds the back of the cover down has jumped off its catch
2. the back of the cover rises and the peg (B) has jumped up onto a ledge (C), so it can’t be pushed down again
3. this puts forward pressure on the button, making it stiff. But also edges (D + E) catch on each other, which stops the button going down, either when the seat is clicked back into the upright position, or by being directly pressed.
Removing the cover:
Release the two long front clips (F) by pulling the seat foam back on the outer side of the cover (G) to see the bottom of the clip (H), and pull it gently outwards with a hooked tool (mine is an old bike spoke) to jump off its step. Repeat on the other side (with headrest removed), and the cover comes off upwards.
Preventing it happening again:
Before replacing the cover, make two simple design changes. File a chamfer to the bottom of the peg (I) so that it will go past the guide ledge without catching on it. Also, file chamfers onto the edges (D+E) so that they do not catch when the button is pressed down with some forward pressure. (Sorry, forgot to take a photo after filing done).
Replacing the cover:
Offer the cover into the seat vertically. The peg (B) should go past its guide ledge (C) without catching on it. The two front clips will click on, and the back hook (A) will latch when the back of the cover is pressed down into place. Tuck foam in all round as needed. Done.
If luggage knocks the cover up in future, it should just push back again to re-engage the hook (A).
Hope this helps someone.