My passenger one went a few weeks ago and it can be quite a simple fix.
To start with sit in the back seat with the front seat in its driving position. reach down under the seatand find the locking mechanism that keeps the seat back locked (from memory they are located on the inner sides of the seat next to the transmission tunnel). You can access them by putting your hand under the seat from the back and feeling for the cable, if you give it a pull the catch should release and the seat back will pivot forward as it should when it was working!!
Now to fix the
problem, if you look at the bottom of the folded forward seat back there is a join where the front fabric and back fabric of the seat meet. unfold the fabric so you can get your hand inside and give yourself some room. if possible slide the back of the seat up as high as you can but warn you this isnt easy due to two springs that keep the shape of the seat backs!!
if you reach up and find the cable that runs from the handle down, then back up, then down again in an S shape on its side. this cable needs to be kept tight in this shape for the mechanism to work. If it becomes detached or a clip breaks and you end up with a too loose cable it wont release the catch.
the fix i did used two heavy duty cable ties, the 3/4mm wide ones, not the really thin ones as it needs to be capable under a slight load. If you grab the cable as it comes down from the release handle and pull it down as far as you can until you get a nice tensioned curve before it goes back up tothe top of the seat on the opposite side. at the bottom of the curve you have created cable tie it to one of the holes in the seat back frame. I used 2 ties as the distance was quite large but also gave more adjustment. You will have to experiment a bit with how tight the ties need to be for optimum release of the mechanism.
Apologies for my drawing, best i can do right now!
anyway the red is the route the release cable takes. the green is where you need to put the cable ties to put the tension back and create the shape again. As i said above i used a hole in the seat frame that was there to cable tie to, you could use the springy frame foam supports but i didnt think they would be strong enough long term!
since i did the fix ive had no problems!!
hope that helps