This is something that often happens, when a coach moves clubs, he might bring some players from the old club because the player's liking for the game is a consideration, especially if the club is able to bring in the players requested by their new coach, so Enzo saw that there was the opportunity for Kiernan Dewsbury-Hall to become a starter at Chelsea and make Chelsea's game better.
Kiernan's presence will give Enzo more options in midfield and players who do not appear consistently will be replaced by Kiernan who performed quite well at Leicester last season