Do your 2.4Ghz and 5Ghz router WiFi bands have the same SSID/credentials? If so, then you need to manually steer/blacklist the Roam to use the 2.4Ghz band in your router configuration pages, but note if your router is using auto-band steering it should automatically select the best band for the device anyway, depending on the strength of signal.

If your 2.4Ghz and 5Ghz bands have different SSID’s, then you could either manually steer/blacklist the device in the router configuration pages, as mentioned above, or as another option, simply swap the WiFi network in your Sonos controller App network settings (this will affect all your Sonos devices that are not using SonosNet-wired mode). See these links:

Remove a WiFi Network:

https://support.sonos.com/en-us/article/remove-a-wifi-network-from-your-sonos-system

Add a WiFi Network:

https://support.sonos.com/en-us/article/connect-sonos-to-a-new-router-or-wi-fi-network