Not a whole lot. Putting a stutterer 'at ease' would be one hell of a trick ;) Don't interrupt them. Treat them like anyone else. Many posts in this sub are people who express how anxious they are about interviews. Or how they feel their stutter limits their professional opportunities. As such, you *might* assure them that their fluency won't be a consideration for the position. Ideally, if you were to communicate that prior to the interview, it would have the most impact. Sometimes just broaching the topic with the stutterer can add to their anxiousness. Doing so at the beginning of the interview might not be helpful. Just my two cents.