A5 laser mount hardware

I just put together today, but took the bottom roller off the gantry(guess that’s it) because I couldn’t find a way to access the screw holes to mount the laser. Later found out the Z axis slides up and down giving access to the screw holes. But…The laser mount wiggles front to back

How do I make this tighter?

There are typically eccentric nuts that are on the wheel axis that can be turned. When turned the nuts will bring the wheels closer or farther from the rail. Tighten it enough to remove any play between the wheels and rail.