How familiar are you with mixing boards? Is ther any chance you don;t have the send set up right? IN other words, an input to a channel strip, the monitor send for that channel up, then the monitor send master up, and am aplifier connected to that output jack?
But assuming thatis not the problem, access is usually by removing the bottom cover. ANy parts that are on the top side of the board will require the board be removed from the chassis, and that will require removing ever knob on the thing. And I always draw up a color chart so I know where the return what color knob.
I don't know this mixer personally, but I think it is new enough - it is still in production I believe - that the components on the circuit board will be "surface mount" parts. Those are super tiny and requife considerable skill to remove and replace.