From the main menu, press
right to highlight Chronicles
on the right side of the screen. Use
to highlight Battles of Kyrat
On the Choose Game Mode screen, use
to select one of the three modes you'll need for this trophy:
Finish one game each of those modes (Victory or Defeat screen at end). Win or lose, you get the trophy when the 3rd game ends.
There is a 4th game mode, Overrun, that is not necessary for this trophy.