I take the crank arms off the bike
Fit the crank axle end in a vice...maybe wrapped in cloth.
Then slip a long scaffold pole on the crank arm and lever it straight.
The crank may be be at a weird angle. So I get a pipe wrench and use it on the pedal end to get the twist out of it
You can do this when the cranks are on the bike. But I have wrecked a bike frame doing that.
Wont do the bearings any good either.
its more tricky to do the chain side. Especialy if youve got a little vice.
I some times take the crank axle out of frame
Then fit it to the crank.
Put the pedal hole in vice and scaffold pole on crank axle and then straighten.
After every tug check the arm.
Is easy as its the old style straight ones.
So can check with a ruler or the straight side of the work desk