Its one of the things which really is not tameable in the ordinary way. The hair ends up in the condition it is because the chemical breaks down and literally damages the hair. Unfortunately there is no way to mend the hair again. While you could use a flat iron, I wouldnt there is far too much of possibility that you will simply melt the hair as it is extra sensitive to heat.
You really just have to tame it as much as you can with shampoo, conditioner and then some styling.