You need just one Auto485 converter on the PC and you can connect to as many as 255 T100MD888+ PLCs using their built-in two wire RS485 port. You don't need an Auto485 at each PLC to do this.
You will only connect Auto485 to the PLC if you want to convert their RS232 port to RS485 port. In this case you will need a null modem cable to connect the PLC's female DB9 to the Auto485 DB9. The connection is simply 2-3, 3-2, 5-5.
You don't need to program the Auto485 with a node ID (you can't do it anyway) as the PLC's built-in protocol automatically handles the ID in the host link command or MODBUS command using the user-defined ID on both serial ports.
However, if you actually need two RS485 ports on each PLC, we would recommend that you connect the PC to the built-in RS485 port (comm3) for master slave communcation and use the second RS485 port (converted from RS232 via Auto485) for connection to other RS485 devices such as HMI or I-70xx modules.