Kristian Campbell likely won’t appear at first base for the Boston Red Sox. Campbell, who was demoted to Triple-A Worcester on June 20, has spent the last couple of months cycling through different positions — first base, second base and the outfield — in an effort to find his way back to Boston. The Red Sox will soon be taking one of those assignments off his plate, though. “First base was an immediate trial to see if that could work,” Red Sox senior director of player development Brian Abraham revealed during his appearance on “The Pesky Report” podcast on Tuesday.