Take a look in the cabinet above the hutch on that wall. The back wall of that cabinet my have a couple of screws holding it in place. If there is screws there that is an access panel to your plumbing lines and the shower fixture.
Another option is to remove the back wall of your basement, pass thru storage, and that should allow you access to those lines that go up into that wall.
My Northpoint has an access panel in the cabinet for the shower fixture. I've had to pull it off to replace my shower fixture.
Give that a whirl and let us know...
2017 North Point 375BHFS
2015 Silverado 3500HD Crew Dually Dmax 4x4