You will find this is a bacterial infection. Go to a pharmacy and buy an anti-bacterial wash. It needs to be anti-bacterial, not anti-septic.
You will find that the pharmacy has anti-bacterial soaps that doctors use to wash their hands. Or they also have antibacterial fash-wash soap for acne.
Use this soap twice a day and the rash should lessen within a couple of days, and completely disappear in about three weeks. Keep using the soap until the WHOLE rash goes or it will just "grow" back again.