Before you tear into the wet bay, it's not going to be fun, are you in an area with freezing or below freezing temps? You may have some frozen water in the lines preventing the valve from turning. Hopefully that's all it is and warming it up with a heat gun or hair dryer may do the trick.
On my rig each valve is screw to the wet bay face panel, then the panel is screwed to the walls of the cabinet area on the sides. You'll have to remove all the screws, then the face panel to then expose all the plumbing and valves.