how do I get the seat up so it can be fixed

I have had this happen a couple of times. You will need to remove the plastic cover on the back of the seat base it will have a number of screws in it. then you will see 2 zippers on the outside of the seat base which allow the lining to be zippered away for access.
You should then be able to see the cable which will have come out of it's stay or in my case the handle had been pushed past the metal lug that is designed to stop it going the wrong way and unseating itself.

Problem fixed all good

Interesting question. I have just purchased a 2002 pajero and cannot get the back seat to flip forward after the back of the seat is folded forward. I contacted the previous owner and he said he only ever had the seat base forward once and had never tried since as it would not move. I too am looking for an answer. You are right in saying there is no room to look at the set up, i even tried a pinch bar as i thought it may just be stuck, still no movement, at least you know the seat can't fly forward. Sorry i don't have the answer.

First thing was to get a short Phillips head tec bit and a small spanner t5o turn it with .My problem was the seat on the right side so there were 4 screws i had to undo in the back of the base ( the only ones you can get to ) Using 2 tyre leavers to prize the plastic base down and then 2 wedges to hold it down . Next was to jiggle each side of to seat to see which side was stuck . Looking in the gap there is a 20 mm long pin sticking out 200mm in from the rubber flap near the seat hinge on the right side for the first one 450mm in for the second one 50mm down from the round bar that runs along the top of the seat base you need to get a heavy piece of wire bending a sharp hook in it ,I had a extra long pair of pointy nose pliers that did the trick . Grab hold of the pin and pull towards you (it takes a bit of pulling to get it to release )
I used a hole saw to put a 25 mm hole on either side and bought 2 rubber plugs to go in them just in case it happens again REMBER TO GET TO THE FUEL PUMP IN THE TANK YOU HAVE TO GET THE SEAT UP TO REMOVE THE INSPECTION PLATE INTHE FLOOR