Talk directly to the person, ascertain what he or she wants, and determine how best to deliver it by consulting with the person. This may sound very simple, and it is.
Appropriate interaction is common courtesy and common sense.
Hearing aids are an unreliable indication of how much a person is able to hear. Many deaf and hearing impaired people do not wear hearing aids. Otherwise, both you and the person who is hearing impaired will feel awkward. Don't assume help is needed. Wait for a response from the hearing impaired person.