This is a story progression achievement, and you will know when you are on the correct mission because it will be your first Assigned Master Rank 3 mission.
You unlock this achievement for defeating the Barioth. The way the game works is you typically can't use a flare to summon help until you've actually encountered the monster, and by then it is usually too late.
My suggestion: Quit out of the expedition once the cutscene plays for finding it, then post the mission and this time you can use an SOS flare to summon help. You will need it.