Navian heater clean procedure

I have a Navian NPE 240 tankless water heater. It has a small .5 gallon tank and a recirculation pump. Its time to flush the system for the first time. Is there an override in the system so I can use the recirculation pump in the unit to do the flush?

It does have flush valves, I installed when I installed the unit. My question is there a way to use the internal recirc. pump to do the flush and not have to have an external pump. ie only run the internal pump in the heater?? I was thinking there might be a pump test or flush mode built into the logic on the controller.