I've cleared the three corridors in area of all enemies, but I'm not sure how to get the fork to lower?

Level: Claustrum Libri.

Hi:
When you reach the room with the three doors dont enter immediately on the yellow square on the grond, let it spawn enemies and will spawn a slime-like caged in pillars. Shoot it to free the slime and then shoot the slime. One of the doors should open. I have not finished that part but i believe there will be no problem with the other doors.
Bye.