Interact with the Mission Board near the Korriban Departure Shuttle to receive this mission:
[Heroic 2] Armed and Dangerous
Acolytes, a warning: only the strongest will become Sith. Korriban's tombs hold many dangers, but none so great as madness. Anyone can be lost to it. The tomb of Tulak Hord is now haunted by one of the lost. Lord Sundar entered the tomb long ago and never returned. Madness has turned him both savage and bloodthirsty. His presence defiles the sacred stone around him. Acolytes who truly wish to prove their worth will rid the tomb of this taint. Deliver Lord Sundar's signet ring here, and you will be rewarded.
After accepting the mission, check your mission log. This is a repeatable quest that can be done once per day. It is reset in the morning.
"A powerful and dangerous Sith named Lord Sundar has gone mad and now roams the tomb of Tulak Hord. If you can eliminate him, you have been promised a great reward. Enter the Burial Fane in the tomb of Tulak Hod and defeat Lord Sundar in combat."
This is a Level 8 Heroic 2 mission, so you should do it in a group. If you are level 10 or above and have a companion, you should be able to solo it.
Your task is to defeat and search Lord Sundar. Enter the Tomb of Tulak Hord, and open the map. Work your way to the Archives, and there to the Buried Fane. Inside, it will tell you that enemy reinforcements are arriving. There will be several groups of enemies you will have to defeat before reaching Lord Sundar, including Mind Controlled Troopers (BOSS). Kill them one at a time, taking care not to pull additional groups while you are fighting one of them.
Once you have cleared out all the groups, kill Lord Sundar himself. Then loot him for Lord Sundar's Signet Ring. Deliver the ring, as proof of his demise, to the dropbox outside the Sith Academy to claim your reward.
This concludes the heroic mission "Armed and Dangerous".