Chernobylite (EP)

In order to get this quest you had to keep Kozlov alive and let him go in the "Kozlov Kidnaping" quest.

***However, If you were like me and had Kozlov killed and went on to complete the game you can still get this achievement. Load a game save to the morning before the Heist (Final Mission). By this point in the game your workshop should have access to Chernobylite upgrades. If you have access to a Radiation Chamber, you can use this to self-annihilate yourself. Upon your death you can change your memories of the choices you have made in the game previously. I simply went to the memory where I killed Kozlov, and changed it to where I spared his life and let him go free.

Upon waking up you'll need to complete at least one day, before getting the mission. I just stayed in my base and sent the rest of my squad out to complete missions. As soon as they got back I went to bed, woke up the next morning and received the quest from Kozlov on the radio.

The mission takes place in the Red Forest:

1st Action - Meet Kozlov. For me he was near the railroad tracks. He asks you to travel to the crashed helicopter in the Northwest corner of the map.

2nd Action - Go to the crashed helicopter, open the side door, and restart its engine. This triggers an underground bunker to open up. The nose of the helicopter points to the bunker entrance. Enter the bunker.

3rd Action - In the bunker you'll find some surveillance equipment. Interact with one of the terminals.

4th Action - Return to General Kozlov and continue to question him. After questioning him you can "Challenge Him" or say "You Believe Him."

Either choice should grant you the achievement.

However, this ultimately cost me one of my team members (Sashko or Olivier), so you might want to save this achievement for last or reshuffle your memories again.