how data can be fetched from ac800m controller to compact hmi 800 without using CN1 CN2 ports
I canot think of any sensible reason for doing this. However ....
The OPC server connection is only avilable through CN1 and redundantly through CN2. If these really are not available use some other communication interface, like modbus serial, modbus tcp etc.
Of course the OPC server can be connected to by several different OPC clients, so really, thats the way to do it.
From OPC, you can take the data through number of ways. But in order to read the opc you need a valid TCP/IP connection. Without TCP/IP if you want you can try using com3 port - Modbus communication. But i guess even this will not work for you without setting IP into a controller.