Nathan Fielder is back in front of the camera with HBO’s “The Rehearsal.” On Wednesday, the pay cabler released the trailer for the new show. In the series, Fielder visits real people who need to undergo a difficult conversation of some kind, and helps them meticulously “rehearse” the event. Using actors and a construction crew to replicate where and how these talks will be held, “The Rehearsal” explores potential scenarios for each event, with Fielder treating the experience with the utmost seriousness.