The thing about this situation is that even if they succeed in opening the stupid lock, what does that get them? Shot shortly after they would have drowned? Or maybe before, one of those things is quicker than the other...
Regardless, if you're in a hole filling rapidly with water, and are being prevented from exiting that hole by a child's puzzle, obviously you try and solve it.
It's not even that hard, or it wouldn't be if it weren't above them, and only able to be accessed by a narrow ladder that he and Valerie are both trying to fit on. Markus expects it came with some sort of tool that would slot around the circles and could be used to rotate them, which their captors have left out. They're making do instead - barely - with their forceps.
It takes long enough, this way, that even though the puzzle itself is infuriatingly simple, the water gets up to Elena's knees, down where she's stabilizing the ladder for them, and then her waist, and eventually she can't maintain footing on the bottom at all; Markus has to switch to grasping the grate above them and bracing the ladder with his legs so Val can keep working on the lock.
The working part of the lock is facing straight down towards them; their captors can't see it. One of them dips out to use the bathroom, confident that he'll be back in time before the actual drowning starts, and the other one... seems to be nodding off? Did Val actually manage to get one of them with some anesthesia as they were being put in here? - In any case, she's managed to get all the pathways connected, and the lock falls open.