Actually it's a tough prospect to straighten a shaft, I've had mixed results. But, for what it's worth, here's my method:
Fold up two paper towels several times, and put one each under the ferrule and joint, to create a little space underneath.
Position the shaft so the high side is on top. Place a towel on top of the shaft to protect, and a couple phone books on top. Leave it overnight and play with it or just sight it next day. Sometimes you have to repeat this several times. To be honest, this has worked for me about one out of three or four times, so it's not foolproof. Usually, the wood wants to return to where it was. But, for what it's worth, it has worked now and then.
All the best,
WW