It is possible that the baby's rash is a result of the fever they had yesterday. If the baby does not have any other symptoms and is generally in good health, you can try hydrating the affected area with a fragrance-free moisturizing cream as needed. Using a fragrance-free soap during bath time may also help. If the rash persists or if you have any other concerns, it would be advisable to consult a healthcare professional for further guidance.