Ok this just happened to me so I thought I'd give my results on this old thread.
My passenger seat would not tilt forward when the lever was pulled up.
A little investigation showed that there are two latches at the base of the seat one on each side behind the plastic bits at the bottom.
Looking at the side of the seat behind the plastic you can see a silver cable that hooks into the black metal frame of the seat. For me this cable was too loose on the driver's side.
I could unlatch the seat if I lifted the lever to unhook the other side and pushed the metal bit that the cable was hooked into at the same time - and then it would tilt forward.
To effect a repair you need to make the seat tilt forward.
First open up the seat...
With the seat tilted forward you can see the 'seam' of the join of the front and the back of the seat's fabrics.
Be gentle but firm using nothing sharp and prise the back fabric away from the front fabric.
I cannot describe this better sorry - basically the back fabric is secured to a length of plastic rod. This rod clips into a U shaped 'open tube' which is attached to the front fabric!
(Sorry my camera was not working when I did this). Anyway, prise gently and firmly ant you should be rewarded with the back fabric unclipped from the front fabric.
Ease the seat cover up a bit so you can see inside.
The uncovered cable that is causing the
problem becomes a covered cable inside the seat and snakes across to the other (lever) side of the seat.
It then becomes uncovered again after a large white plastic block
For me the
problem was that this plastic block had worked loose from its mount.
The plastic block has clippy bits on it - kinda like the way camera flash guns clip onto cameras.
Well, I was lucky my plastic block slid back onto its mount quite easily.
Once in place the
problem was cured.
I carefully eased the seat cover back into place, unprised (reprised?

)the front fabric to the back fabric and walked away laughing.
All in it took me 15 minutes, I didn't need any tools and it looks fine.
The problems I can see you struggling with are:
Not seeing
how to get the seat to tilt in the first place - because you cannot see the cable to know what piece of metal to push - compare with the other side - other than that good luck!
You might have to reconnect the cable to the latch mechanism - this should be straight forward - there's really only one place for the S shaped end of the cable to go and it looks the same as the lever side.
Unclipping the fabrics - just be patient and do not use any tools - you might need stronger fingers - ask a friend.
The fix itself might not be straight forward for you - if your plastic block is knackered you may have to improvise a solution - maybe by glueing it in place or using cable ties or a combination of both - good luck.
Not much more to say now - I hope this helps.