Conan O’Brien returned to “The Tonight Show” on Tuesday for the first time since exiting the job in 2010. O’Brien, who was on the show to promote his upcoming Max series “Conan O’Brien Must Go,” spent much of his time reminiscing with host Jimmy Fallon, 49, about his time on the show. “It’s weird to come back,” O’Brien, 60, told Fallon.