After you stop the attempted Cerberus coup, Primarch Victus sends Shepard an e-mail giving Shepard this assignment.
First, go to the Citadel Embassies floor and go to the Spectre room. Use the Spectre Terminal to receive a location on Din Korlack.
Then, talk to the turian guard who's at the Office Suite in the Citadel Embassies. He will let you into the office.
Once you have listened to all three recordings, on the opposite side of the room you will find an ear piece. There will be a cutscene and then you will end up at the Presidium Commons. Head up to either Apartment 80 or 94, the ones at the far ends of the hall. Whichever you try first will be the wrong door. Open the correct one to find Korlack either being guarded by Zaeed Massani (either alive and well after killing the following two mercs or dying on the floor depending on whether or not he was loyal), if he survived the Suicide Mission, or being threatened by two mercenaries, a human female and krogan male. Shepard will respond appropriately.
Note: If you can’t open the door, reload a previous save data.
After the cutscene, there will be a choice between saving the colony or gaining the Volus Bombing Fleet as War Assets. Alternatively, if you completed Zaeed: The Price of Revenge and received his loyalty, you can choose a Paragon or Renegade option that gets you both. Upon completion, you will gain 210 experience, 5,000 credits and morality points depending on your conversation choice. If Shepard chooses to not warn the colony, the Turian Sixth Fleet will suffer losses during its defense.
If Zaeed is loyal, you will be able to find him in the refugee camp and recruit him as a War Asset. If he was not, he will be slain protecting Korlack, costing you not only the Asset but the Persuade options in the ensuing conversation.