Be a bit more precise, please ! If you mean "If you betray me, I will turn you in" Then I would translate it into : "Si tu me trahis, je vais te dénoncer à la police". So here, I said "I will talk about you to the police officiers" instead of "turn in" because it's a more common way to say it. If you mean "this criminal turned himself in" I would translate it by "ce criminel s'est rendu". If you mean "it's time to turn in" (meaning time to go to bed) I would say "Il est temps d'aller au lit". Is it what you meant?