Here is my video playthrough, but for more specifics:
1. Start the mission, and gain access to the elevator via the receptionist.
2. Do what you need to do on the first floor, then go to the second.
3. Walk to the far right, past the meeting, until your camera moves you to an organ player.
4. Eventually he will turn around and play the organ. Just listen.
5. Then, you'll get the option to return to the balcony.