My daughter has chapped broken skin in her underarm area and it is darker than her regular skin tone. she is 11 years old. what can i put on it to hel?

Treatment would: depend on what the cause is. It could be an irritation from clothing or an antiperspirant, or any topical products applied. I would recommend having her doctor examine her so a proper diagnosis can be made and then proper treatment recommended. Meanwhile, you could try applying Aquaphor, which is an over-the-counter healing ointment.

Plan: Use moisturizer daily after shower. Like Aveeno lotion or Vaseline or other cream. But daily!!!