If the blade is what is twisted, remove the blade and place it in a padded vise. Lightly bend it in a vise using an adjustable wrench to correct the twist. Put a rag around the wrench so you don't scar up the rear leaf as you apply twisting pressure.
I think it should bend easily (like a main spring).

Don't tighten the screw (attached to the gun) as this won't straighten the blade out.

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