This will come with naturally playing the game but I do have a few steps to ensure fast gain of this achievements.
-Get the level 6 agency perk "Loot Lock Search Program. This allows you to see loot boxes with your scan ability.
-With said scan ability, press Y frequently to see the purple highlights.
-Look for large yellow loot boxes, often found in the LEGION lair scenarios done throughout the story. There are standard square sizes and larger rectangular sized boxes.
Eventually you'll stumble across one for this easy achievement.