You’re literally and figuratively dropped in it at the start of this as you’ll directly continue from the previous quest. You’re facing a Corrupted Behemoth with no weapons or armour, not a great scenario. Your strategy here is to stand behind the pillars that hold up the platform in the centre and let the Behemoth charge into them. After this happens twice, a cutscene will trigger in which you’ll get your equipment back.
Now the fight is a bit fairer at least, although by no means easy. The Behemoth is a tough nut to crack, but there’s always a way. If you can load up multiple arrows at once, do so with Tearblast arrows and hit both sides of its face to take out its more damaging ranged attack, then start putting down blast wires and traps and goad it into charging you. If you’re lucky, a couple of rounds of that will take it down. If not, use a Warbow to hit the canisters on its rear for extra damage.
When it goes down, there will be a cutscene and that’s this quest complete.