I tried straightening a ballscrew myself once, made a jig with a dial test and everything. Its an art and one I did not have the patience to master, check out some of the youtube videos there are a few out there. Bottom line is you really need to have a good setup with jigs and some way of applying lots of pressure to isolated points on the screw. You could try getting the worst of it out by eye using a flat surface and a vice, it would be an amazing skill to learn and something that would stand you in good stead for repairing and building machines in the future. Most ballscrews come bent shipped from the factory espically if you buy rolled, and I think straighting is considered part of the machining process if done correctly.