20 years ago I did this to a shaft that had a bad 1/8" + warp to it.
I put a piece of scotch tap around the joint end and after rolling it on a table a few times, I put a + sign on the high side and a - on the low side.
I took a an old fashioned tea kettle and steamed the shaft for a few minutes.
I then set the shaft between to kitchen chair backs with a leather belt looped around it, + side up, with about 5 or 10 pounds of weight hung from the belt.
I would let it set for a few hours and then check it.
I found that it would spring back some after taking the warp out, so I would let it over warp and then let it rest for a day before making any adjustments.
I got it back to about a 1/32 warp before I stopped working on it.