Sorry for butting in Graham.
KOM Yes you can do it yourself. Find the (hopefully) braided flexible pipe. This is the filling loop. It should have an isolation valve at both ends, one from the rising cold water main and the other into your pressurised system. First find these things. The valves often have little plastic levers that are at 90 degrees to the pipe when closed and in-line with the pipe when open. Then you open the valve at the pressurised system end if it isn't already open then, while watching the pressure gauge, slowly open the isolation valve on the rising main end. Let some water in then close the valve to let the gauge stabilise. Repeat until you get to the required system pressure which as Graham said is normally 1 to 1.5 bar. If you have difficulty watching the gauge and operating the valve at the same time, get an assistant to do one of these things for you. Good luck!