dermatitis or balanitis(due to an underlying infection (bacterial and fungal as well as other organisms) .
You may try calamine lotion on the rash.You should also maintain hygiene and try to keep the area clean and dry, wear loose-fitting cotton clothing. Also use an antibacterial soap or mild soap like dove.Avoid any kind of cosmetics.You can also use calamine lotion or a mild steroid cream like dermacort on the rash.If the rash is itchy, you can take some antihistaminic like Benadryl or Claritin.
If the symptoms persist then it will be best to get it evaluated from a dermatologist.
Hope it helps.Take care and pls do keep me posted on how you are doing or if you have any additional queries.Warm regards.