If the vice is FIRMLY bolted to the bench and the bench bolted down, find the 'bend' point, secure into vice. Take a reasonably tight fitting long pipe, slide over the shaft and bend it 'some'. Look what happens,odds are you'll need more. It's a 'do and see' operation.
If the vice isn't strong enough... got a pickup with a 2" hitch? if so and the receiver is hollow, use it for your 'vice'. Same idea, bend the shaft in the opposite direction of the bend.
Sometimes you have to think outside the box, get creative, I've driven my forklift over steel to 'rebend' it