The best advice I can give is look at how entertainers get random audience members to relax and engage in front of huge audiences. Many people lock up in such situations and can barely say their own name, yet with the right approach it’s a non issue.
Compare that to the rapid fire technical questions I have watched people get into and it’s obvious what’s going on. Someone fumbles something and then gets flustered and shuts down. But, pepper the exact same questions into a larger conversation, perhaps going so far as to occasionally complement them, and shockingly they do better on the exact same problems.