Thank you for the very good question. 

You need to create a configuration file in Excel. You can download the latest template of the excel file and create your own configuration based on it. 

Also, we have made HOWTO how to read meter data and transfer data over IEC 60870-5-104 protocol to SCADA. 

https://wiki.elseta.com/books/how-to/page/modbus-rtu-to-iec104-protocol-conversion
Please take part in Modbus from here and if you have more questions write them down here.