Play Us a Sad Song, Claude
From Halopedia, the Halo wiki
Play Us a Sad Song, Claude is an achievement in Halo: The Master Chief Collection. It is awarded for changing the Club Errera Easter egg music to Siege of Madrigal in New Alexandria. This is achieved by first activating the Club egg by finding the switch nearby the hospital. Then before going in, fly to the top of the Club Errera building and on the roof a switch should appear behind an arch of ventilation pipes. Both this and the HBOrg Special achievement can be achieved in succession if you go into the club to get the first achievement. Leave before the NPC's turn hostile, activate the switch on top of the building, then head back inside the club.