In the GOT settings under enviromental settings look for screen switching devices.
By default already GD100 en GD101 are setup for Base and windows screen, The superimpose window you have activate and give a Device.
After that you can use it
You don't have to define the network number and station number in GX works 3. this is only needed when having multiple FX5 station in one GOT.
All you need to do is define the IP address in GX works 3.