See post above for first steps. Next. Turn power off, switch valve to backwash.
Turn on. Water will gush out of that hose. Watch the water in the sight glass until it runs clear. (Or at least no particles. Your water may not be "clear" in color...) this should normally take between 1-3 minutes depending on how dirty the filter is, but today, lean towards a longer period so we know it's clean. Turn off.
Switch to rinse. Turn on. Watch sight glass until water becomes clear, but at least 60 seconds.*
Turn off.
Switch valve to filter. Turn on. Record the psi as your "clean" psi.
*Some people only rinse for 30 seconds, but since we are trying to establish your clean psi, go for it.