First set the printer on its side, with the X Belt tensioner (opposite of X motor) touching the table.
Remove the screws circled in red and blue.
Longer screws are mark in red
Shorter screw are marked in blue
Slowly set the bottom cover down in front of the printer and unplug the fan from the motherboard. Then set the bottom cover aside.
All axis Vrefs potentiometers are circled in red above E, X, Y, and Z.
Ground reference point is marked by the black arrow