Complex sentence: The mentalist then asks the spectator to pick one of the two books; if they choose the force book the mentalist says "ok you take that book" and hands the force book to the spectator.
Split into simpler sentences: The mentalist then asks the spectator to pick one of the two books. If the spectator chooses the force book, the mentalist says, "Okay, you take that book," and hands the force book to the spectator.