Switch allegiance of Helghast Sentry bots as Hakha

As Hakha, you will need to hack, by pressing on a small console, a Sentry Bot, and make it attack the Helghast instead of you.

Chapter: Misty Waters

If you miss that opportunity, you can also try it on the first level of the chapter, Hidden Pasts. After you reach the gates of the Missile Base, you can enter it through a path created by some pieces of rubble. You will engage in Close Quarter Combat with two Helghast Elites, and after you kill them both, look for a switch nearby. After activating it, you will have a new temporary ally, and a shiny Bronze trophy.