@Nickson you've taking apart your trendline's havent you? iirc
I have indeedy!
Removing the rear plastic cover requires basically stripping the seat down to bare metal (the backrest part anyway).
Start by carefully, and I mean carefully, peeling back the seat cover around the edges, making sure to keep hold (or pop back on) any of the metal clips that help to hold it on.
Pop out the plastic harness eyelets.
Keep working your way around the cover, making sure to free off any sections around the edge where it may be clipped on. Don't forget about the bottom of the cover where it tucks underneath from the front to the back. For this, I found it easiest to adjust the seat so it was leaning all the way forward and release it from the back.
If I remember correctly, the centre of the seat cover, the seam where the leather bolsters transitions into the alcantara, there are spines and more metal clips which attach to the metal frame (IIRC) through the yellow seat foam. (By this point the cover should be loose with just the centre holding it on - all of this is from memory, so please don't take it as gospel, just general guidelines). Carefully pop all of these clips off, which should release the cover itself, just pull it off of the seat.
Additionally, I've just noticed there are clips around the "Recaro" branded leather part as you can see in the image below, again, clipping to the plastic cover on the rear of the seat. Take care when popping these off.
You should then be left with the yellow foam and the remainder of the seat.
Slide the yellow foam off (I can't remember how easy this part was, but it probably wasn't too difficult!)
Then pop the plastic backrest and slide & tilt handles off of each side.
Then there should be 4 or so screws and a few hooks holding the plastic cover on.
Voila.
I did mine just to fix the slide and tilt mechanism by replacing the cable. Hell of a job, but worth it (IMO) once it's finished and back together!
Feel free to PM me if you need any help!
Best of luck!