Please note that on the mAX Pro W31, the home network cannot have separate bands for 2.4GHz and 5GHz, as it operates as a combined network for both frequencies. Similarly, when you create a guest network, it will also be a combined network.

Please refer to the link, where you can find the steps to enable and create a guest network,

http://arris.force.com/consumers/articles/General_FAQs/mAX-Routers-Guest-Wi-Fi-Network-Setup