Talk to Dr. Zed to begin the mission, where he’ll offer you a job to be his assistant in the surgery he’s about to do. When prompted, melee the poor fool on the table to make an Eridium Shard pop out of him. Pick it up and Zed will mention to bring it to Tannis, who’s located on the first floor of Roland’s place. Talk to her once, then one more time to finish the mission.