Reformation

Reformation is a main quest in the Fallout 4 add-on Far Harbor.

Detailed walkthrough
During the quest The Way Life Should Be when confronting DiMA about killing and replacing Captain Avery, the Sole Survivor can agree to keep it secret. After that, DiMA will suggest a plan to replace High Confessor Tektus with a synth to ensure peace between the factions. Agreeing to the plan will start the quest.

The Sole Survivor first tracks down the holotapes of the previous high confessor, Martin. These holotapes are located in his hideout within the pump control station. Once retrieved, one must and bring them back to DiMA, who will provide a doctored version. Heading back to Tektus and showing him the fake version will result in Tektus believing the old confessor is coming back to take over his position and suggests speaking about it further inside the command center.