Aanish,
Strongly recommend you do not attempt to heat straighten.
Distortion rectification is "usually" dealt with in your project specification - client approval required.
There are numerous ways of resolving without putting uncontrolled heat into a weld and possibly damaging the mechanical properties.
Some clients allow a "tig-wash", some allow partial excavation on one side and rewelding, some just require it to be punch-listed and the site contractor will offset the final flange weld to suit.
Whatever you do - make sure the client is informed.
Cheers,
Shane