A red patch is likely caused by friction from an ill-fitting hearing aid or moisture buildup leading to irritation. Do not use medicated drops without an evaluation. First, leave your hearing aid out as much as possible to let the skin heal and keep the ear dry. Next, consult your doctor; they may prescribe a mild steroid drop (like hydrocortisone) for inflammation or antibiotic/antifungal drops if there is an infection. Finally, visit your audiologist to have the hearing aid shell adjusted. A proper fit is the best way to prevent this from recurring.