Had a look, yeah, pain in the ar$e.
ETis states that you have to take off the height adjuster, Trim around the side of the seat base, disconnect various other bits etc etc...
I`d say, tilt seat back forwards, under the seat back there is the crease that the two plastic trims sewn into the fabric "Lock" together, try have a look at the end to see how they lock together as its hard to explain ( a little like to C shapes with a barb running along, interlock into an S,kinda.), a small screwdriver to prise apart starting from one end and you MIGHT be able to pull the cover up high enough to renew the arm rest pivot, which is possible Pop rivotted on. Also you`ll have to remove other bits which are entangled.
If you are succesful, it is yet another battle to get the cover taught enough to make the plastic trims meet and lock back together.
So, to sum it up, pay someone else to do it if possible!