You need to load chapter 44 , right after you go through the vault-like door and drop into the water, you see the
again.
Flee to the right and climb up, then go the right and back into the water through the lid in the floor and wait until "it" almost gets you again.
Climb out und run back to where you came from, jump into the water and dive in the direction "it" came from.
Go up to the surface and to the left to find the machine for the achievement.