Before we get started, we will refer to your modem or non-NETDUMA router as your 'hub' in this guide.

Disconnect your NETDUMA router from the hub so that it is isolated.

Then using an Ethernet cable, connect port 2 at the back of the NETDUMA router to a computer. Open a web browser on that computer and enter in the URL bar at the top. This should take you to the NETDUMA interface. 

From there navigate to “Settings > LAN”. In the "Host Address" box at the top you'll see “1”. Replace it with “88” (without the quotation marks). Your page should look like the image below. Click apply.

Power off both your hub and your NETDUMA. With an Ethernet cable connect port 1 from the back of the NETDUMA into any other port on the hub. Power up the hub and after one minute, power up the NETDUMA. Now, reconnect all the devices to your NETDUMA and everything should have reverted back to factory settings.