It's been a long time since I had one apart.
I would remove the seat and also remove the back for easier access, personally. You need a hog ring pliers and hog rings to do the job. I have that stuff here somewhere.
You'd have to see my garage to get that one.
Unzip the cover and you'll see that the ends are tacked to the seat with hog rings. Much easier to cut them and get them out. The long bars also have hog rings and they loop over a wire in the seat back. They keep the cushion folded into the groove beside the bolster.
As you remove anything attached, pull the cover up by turning it inside out. There'll be more rings at the wire mentioned above (just under the head rest). Once you get going it's pretty easy to see how it's put together.
If your bolster cushion is badly mangled (the wire frame tends to poke thru) then you can either get another or patch with foam and duct tape it together to get the right shape. It will be under the cover.
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