At the beginning of Facility, you will crawl out of the air duct into a room. This room contains the locker with the Lolife, but, for now, it is locked. To unlock it, you will need to wait for a Nazi to retrieve it. However, he will not move until prompted by the player. Leave the room until you can see the Nazi in their room. One will be abusing another. After the latter runs away, the other two will talk about a 'customised pistol', then one will leave. Follow this one through a door back into the first room, and wait for him to open the locker. Once he does, kill or knock him out and pick up the pistol to unlock the achievement/trophy. There is a video guide below if you are having trouble finding it.