Once a screw is bent your chances of getting it truly straight are remote but you can probably improve matters to the point where it works. You need a good solid work bench, five blocks of wood with grooves across the grain, two G clamps and a straight edge.

First you find where the bending needs to happen and clamp a free end of the screw to the bench using two blocks so it bows upwards at the bend. These first two blocks stop it turning and stop the G clamps slipping off while protecting the thread.

Mark the top of the bend in felt tip so you can find it again if it should turn rather than bend.

Then it's two blocks underneath, either side of the bend, one in the middle on top and away you go.

The trick is to go slow, get a feel for how whippy it is. A little bending and a lot of checking with the straight edge.

Don't try to save time by skipping on the grooves, everything will roll about and stress you out something chronic.

You really should not have this problem, good luck

Robin