You do not download firmware from Nokia. You receive it from your ISP.
To understand the physical features and proper placement layout of your exact hardware, you can read the Nokia Fastmile 5G Gateway 3.1 User Guide . FastMile 5G Gateway 3.1 User Guide - Nokia nokia fastmile 5g gateway 3.1 firmware download
: If you use the Nokia WiFi App and device details aren't appearing, try deleting and reinstalling the app to refresh the gateway's status. You do not download firmware from Nokia
If you desperately need the previous behavior, your only option is to source an identical gateway with older firmware from eBay or a friend (unsafe and not recommended). nokia fastmile 5g gateway 3.1 firmware download