Dampen the scorched area of the dress shirt with water. Sprinkle cornstarch over the stain to cover it completely. Let the cornstarch dry on the surface of your dress shirt, and then brush it off into the trash.
Treat any remaining scorch mark stains on the dress shirt by moistening them with a few drops of hydrogen peroxide, followed by a few drops of ammonia. Use an eye dropper to place the peroxide and ammonia directly on the scorch stains. Allow the combination to soak into the fabric for a few minutes for a light stain and up to one hour for a darker stain. Add a few more drops of peroxide, followed by ammonia, to keep the fabric moist the entire time.
Wash your dress shirt in the washing machine, using laundry detergent and oxygen bleach to remove the substances used to take out the scorch mark stain.