i have a network with an elevated tank & want to control the flow & decrease pressure which come from the pump station to let the elevated tank cover the difference at the early period of the network
You need to give us a little better description of how this is connected and what you are trying to accomplish.
Are you trying to control the flow from the pump so that you don't overflow the tank? If so, just turn the pump off when the tank reaches a high level. No need for a flow control valve.
Do you really have an actual valve that behaves the way that an FCV in WaterGEMS behaves? In most cases, the real valve would be controlled by pressure, not flow because flow measurement is much more expensive than pressure measurement. The way you control flow in a real system is controlling pumps, controlling demand or using a model valve that behaves like the real valve that you will install.