I helped my friend installed Volumio on Raspberry 4，and installed needed Plugins. How can I reset the Web Settng back to beginning? make Volumio to a Hotspot, so my friend can set WiFi connection to his WiFi.
Have you tried System Settings | Run First Config WIzard?
Another option might be to turn on Hotspot Fall back under Network settings:
This turns on the Hotspot if a wireless network can’t be found.
Of course you cannot do any of this if your Volumio isn’t on a network in the first place, so you might need to use a wired network connection to make the changes. That’s what I had to do with a Volumio running from an USB drive on my laptop as my WiFi adapter wouldn’t allow hotspot operation and WiFi access at the same time.
Hope that helps,