And keep in mind the key word here is 'twist'. The chain stays on most bikes are not parallel with the chain path. The stock tensioner, when bolted to the chain stay (frame) will position the tensioner wheel at a slight angle to the chain. That is the angle you want to remove. Viewed from the rear of the bike it is easy to see how much 'twist' the bracket needs to align the wheel with the chain. Depending on the bike quality, I'd be careful trying to twist the bracket with it attached to the bike. A bench vise is the preferred method but not a tool everyone has. If you have to bend it on the bike, go slow and make sure the bracket is bending, and not your frame. Heat is not necessary.
Tom