“Turn into” means “transform into.” Your fairy godmother can turn a pumpkin into a coach. The way to instruct someone to submit a document is “turn in to,” with a space between the “in” and the “to”: “turn your application in to the registrar.”

Apart from phrasal verbs, into and in to are pretty easy to figure out. Into is a preposition, which means it denotes a location, and in this case, a movement toward a location. It can also denote some kind of transformation. For example: Jim turned into a car.

"Turn in to" usually means "rotate toward", as when a driver "turns in to the driveway". "Turn in" can mean "submit <something>", as in "The students turned in their homework." "Turn in" can also mean "go to bed", as in "I think I will turn in for the night." Turn into a thing.