RTA 435NBA, 435NBX is a great device for communicating between ASCII device and Controllogix PLC.
Normally, you can find the module ip address by running the IPSetup tool.
If not, you can reset it to factory default by using the pin hole or open up the box inside there is a reset button.
If that still does not work, then connect serially to port 0 using a null modem cable and run MTTTY tool and click connect.
Next, cycle the power and you will see its ip address: