If hand bending won't work, i use a peen hammer on an anvil, striking inside the
bend (ie the concave) one tap at a time.

It's counterintuitive. You'd think you bang on the convex side to shove it back
into shape, as you would with a dent in a fender. But that doesn't work on
spring steel.

The peening spreads steel, and that spreading "pushes" out the concavity. 

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