By creating a separate SSID of 2.4 Ghz
Currently the LEXI Hub only works on 2.4GHz. By default, the AmpliFi router combines its three bands -- a 2.4 and 5GHz band that each support Wi-Fi 6, and a second 5GHz band that supports Wi-Fi 5 -- into a single network, but you can split any of those bands off as a separate network with its own SSID.
Split any of those bands in to a separate network with its own SSID to create a 2.4 Ghz network and then try connecting your hub to it. Ensure you give a separate name to the new SSID which will help you recognize the network easily.
Please refer to AmpliFi support article for creating the 2.4 Ghz SSID.
Feel free to contact us if you need any further assistance.