You may need to power cycle the device into a safe (read-only) image, if you cannot see your device in the NI-USRP Configuration Utility and are unable to reset the IP address.
When you have done this, it will reset the device's IP to the default value of 192.168.10.2.
For step-by-step instructions, you can see the
Why Doesn't the Device IP Address Reset to the Default? section located in your
USRP-2920/2921/2922 Getting Started Guide or
USRP-2930/2932 Getting Started Guide.