The Mass Effect 3 side quest called Apien Crest: Banner of the First Regiment, can be started as soon as you gain access to the Purgatory Bar.
You have to find a group of Turian officers, near the lower bar (point 3), on a red sofa.
Approach them to begin the mission.
When to start
After Priority: Palaven
Description
“A Turian officer needs the Banner of the First Regiment to inspire his troops.
Recover it from Castellus in the Apien Crest, and deliver it to him at Purgatory on the Citadel.”
Reward
Turian Seventh Fleet War Asset
Walkthrough
Access the Galaxy Map in Normandy, and locate Apien Crest in the Milky Way (SW).
Travel west to Castellus cluster and scan planet Digeris to find the Banner of the 1st Regiment.
Head back to the Purgatory Bar in the Citadel and give it to the Turian Officers.
Next side-quest: Tuchanka: Turian Platoon.
