I have a couple 5-year-old inexpensive office chairs(same make/model)
in my house.

On one of them, the seat back has been broken for several years, so it
just flops loosely and offers no support.

On the other, the gas cylinder (shock absorber) that is the center
support post broke so that it won't support my weight. My wife and
kids can sit in it okay, but it just drops down under my weight.

I'd like to remove the good seat and back from the chair with the bad
gas cylinder and put it onto the other chair, giving me one "whole and
good chair" with a working gas cylinder and working back, plus one
"totally bad" chair with a bad back and collapsing gas cylinder.

But try as I might, I can't pull the seat from the gas cylinder on
either chair. The seats just "drop right on" when being assembled,
and I assume that human weight, plus friction, holds them on.

What technique might I use to pull the seats off the cylinders, so I
can put the good seat onto the good cylinder?