Dear Anju,
I know few things that are used to remove the marks and prevent the scars.
Sandalwood oil can be applied on the affected area, but the treatment should be started the first day of appearance.
Vitamin E oil also helps the scars from chicken pox to heal, and it can be used along with sandalwood oil. Those are natural ways of removing the scars, but I think you need some medicine. There is a fluid called Miracle Cure that can also help in removing the scars from chicken pox, you should consider trying it.
Also have a luk at this link...
Hope it helps...
Luv
Tej