Run a temp Ethernet is usually the easiest way. Hook it to your main router’s ports.

am comenting to get notified when somone resolve this issue!

What issue? When you change your wifi you need to tell your smart speakers the wifi has changed.
 

Easiest way is by connecting an Ethernet cable temporarily, as already stated. Alternative is to set the credentials of the new wifi so it matches the previous SSID and password. 

uh, yeah , so there has to be a way other than finding a damn Ethernet cable.   We should be able to change our wifi passwords without this sort of hassle

It’s easy to reconnect all kinds of other devices by just updating the wifi password.  But can’t figure out how to do it with Sonos.

If the other device has a display and keyboard, it’s easier to change the WiFi setup. If it was too easy to change a password, the mischievous teen next door or a drive by hacker would be playing their music for you.

If you don’t want to temporarily wire the unit, then Factory Reset the unit and add it to your system. The other units will adopt this unit. If this is your only unit, note that you’ll need to setup a new system because Factory Reset will destroy your music service registrations, SONOS Playlists, and your local music library index (if any).

I got an ethernet cable.  I connected Sonos unit to my router via ethernet.  My computer was on the same network via wifi.  At this point, my phone app did recognized Sonos unit and I could stream music.   I *thought* that having made this connection would “teach” the Sonos unit the new eero wifi password.  But when I disconnected the Sonos ethernet cable, my phone app would no longer "see" it. I can’t leave the Sonos unit permanently connected to router via ethernet -- because I normally listen to it another room far from the router.  So I am still stuck.

Do you have any other SONOS players?

No

You’ll need to revert to the old WiFi SSID and Password prior to installing the new router — or Factory Reset the unit. Your PLAY:1 no longer supports updating the network without Factory Reset.

Thanks for trying to help.  There is no new router, no new network.    I only changed the network _password_.  Do I still have to do a Factory Reset (with all the repercussions thereof)?