Plugging one of your existing units into router then there should be no reason it doesn’t come up in your controller (it may ask you if you want to connect to exsiting system).  Maybe give it 3-4 minutes to come up after plug in router.

Once it comes up - go to settings...system...network and run the wifi setup wizard (you can then unplug again)

@HKM

Below in the link are the steps you should have followed when changing SSID, Passphrase or router on your network.

https://support.sonos.com/s/article/1061?language=en_US

Question: If you followed the steps in the link are you using a range extender or access point? If so those devices must match your router SSID and Passphrase and not be DHCP capable. 

Thanks to both of you for your reply. I have done everything you both already suggested and it did not work. I finally did “find” the Sonos Connect on the app only for it to reset when I plugged it into the stereo system. I have been giving it 15 plus minutes and nothing happens. I thas been over 2 hours of doing each step that you have suggested and nothing. I uninstalled the app and reinstalled. Now the app is saying to connect to existing sonos 

Yes that is what you want.  Connect to existing sonos

Hi @HKM 

Reserved if “Connect to existing doesn’t work”

I asked it there were range extenders or access points involved in your network. Since you didn’t address it in your reply I’ll assume they are not in play. That said assuming you have followed the directions given by  @Chris  and myself there are two options left IMO:

1. If possible submit a diagnostic, post the reference ID in this forum and Call Sonos Tech Support or contact them via Twitter or Facebook https://support.sonos.com/s/article/141?language=en_US
2. The alternative is to perform a factory reset of all Sonos. However, doing so will destroy all setting and playlists. (This only recommended as a last resort.) https://support.sonos.com/s/article/1096?language=en_US

Let us know how things sort out. 

ok I had to set it up as a new sonos connect. That was the only way that it would work. I had to do thos through the ethernet cable because even when I connected to the Sonos temp network, it would not recognize the connect or network despite sitting letting it sit on the temp network for 4 minutes. Once I set it up as a new devise I was able to set up the wifi network. This was not straight forward at all and nothing in the articles that were on the help page addressed or helped with any of this. Very frustrating that it took 3 hours to do something simple like change a password to wifi. Sonos you need to develop better technology that allows you system to recognize that the wifi password is not correct and just put in the new password rather than go through your ridiculous hoops that ultimately didn’t even help.