Mange is a serious and potentially life threatening condition that should be diagnosed by a vet. Your vet would likely prescribe a medicated rinse of sulfurated lime or a drip-on medicine such as Revolution (Selamectin).
In order to treat it so it will not keep coming back you need to take the dog to the vet and they have a shampoo they will give you and you need to use it as perscribed and in no time the mange will be gone and won't come back again.
