You will have to remove the MIOM from the top of the power unit.
You do not have to disconnect any wiring.

Remove the steel tube from the shuttle valve fitting.
Leave the tube connected to the manifold fitting.

Use a 1/4" union to attach a pressure gauge to the steel tube.

DO NOT attach the gauge to the shuttle valve fitting.

Use the pump run switch to run the pump while monitoring the pressure gauge.

Pressure should be between 3400 PSI and 3600 PSI.

DO NOT ATTEMPT WITHOUT A PRESSURE GUAGE

If pump pressure is below 3400 PSI or above 3600 PSI
The pressure may be able to be adjusted according the the following instructions.

There is an adjustable relief set screw with a jam nut on the side of the pump block.

Use the pump run switch to run the pump.
Monitor the pressure gauge while turning the set screw.

Loosen the jam nut. Turn the set screw clockwise to increase pressure.
Turn the set screw counter clockwise to decrease pressure.

DO NOT increase the pressure to more than 3,500 psi.
When adjustment is complete, tighten the jam nut.

If the pressure cannot be set to 3500, replace the pump/motor/tank assembly.

Remove the pressure gauge and re-attach the steel tube to the manifold fitting and the shuttle valve.
Re-attach the MIOM.