Harry woke up in a room , then a voice asked what's in the middle of Paris.
"R" Harry said, "Correct!" said the voice
"Now you have to find yourself and bring yourself back here" said the voice
"How?" asked Harry
"I'm going to send you back in time" said the voice
Harry went back in time 3 hours and found himself.
Then Harry transfigured some parchment into a baseball bat and wacked his younger self with it knocking his younger self out.
Then Harry used a levitating charm to carry his younger self.
Harry didn't know where the room was.
So he asked Dumbledore and Dumbledore showed him where it was and sent him there.
Harry deposited his younger self there and went off to do his Transfiguration homework.