At the mean time, abandon the wiper completly and clean with cotton and water only; use cottom diaper during the day when baby is awake or leave baby's bottom expose without covering; you can also start potty training, of course, by holding the baby in your arms.
Go to see the doctor(s) and make sure there is no yest infection. If there is, prescribed cream is unavoildable.
Don't use hair dryer to dry the skin. Powder is also not recommanded.
Wash baby's bum with warm water every time you change the diaper. Dry it with a towel. Try to avoid using baby wipes. I switched from baby wipes to towels when my son had rash. It had good effect.