Connect it temporarily by Ethernet then change the wifi details in Settings, System, Network, Manage Networks.

Or another approach is set out here:

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

You have set up a wireless system. If you change the password for your wifi, how could it automatically reconnect? You have to tell it the new password somehow, and John’s post above describes how.

Did your phone/laptop automatically adjust to the new network? No, you had to tell them how to. Sonos is no different, but as it doesnt have a screen or a keyboard its not as obvious.

Controlav firstly I don’t appreciate your condescending by tone.  Please be more respectful.

secondly, Sonos app doesn’t just tell you it can’t connect to the wifi when you change a password on your router and then ask you for the new password.  , it tells you it can’t find the system.  As a result, accessing system, settings etc is not possible.  You have to reconnect which is the task that is not working 

John, thank you I will retry this today to see if I am missing a step.

woyld you expect the app just to ask for the new password after I change it in the router?  Not sure why it can’t find the system?

I wouldn’t expect the controller, and by extension, the Sonos system, which exist on the speakers, and not the controller,  to ‘know’ that a password has changed. The Sonos system  has been told to look for a single SSID and password. It’s telling you that this SSID and password are not to be found, it’s up to you to tell the system, by connecting to it with an Ethernet cable, that it has changed. Or, you could have given it the information before it changed, which would the cause the system to disconnect until such time as the SSID and password are there. 

As @John B suggests, the only way to reconnect to the Sonos system, without using the old SSID and password, is to connect a single device with an Ethernet cable, which switches your Sonos over to a ‘wired’ network, as indicated in the wired and wireless modes FAQ, which allows you to tell each speaker, at the same time, the new network information, so that when you remove the network cable, they know what network to connect to. 

You said, and I quote, “I cannot believe this is the level of technology of a system that cost as much as it does. “. I explained why, in as simple words as I could muster.

John, I have managed to setup one speaker using the cable to the router.  I now try to add a product and through the system area and to the product but it doesn’t see my sound bar, other speaker or sub.  I have unplugged the soundbar, sub and speaker and then plugged them back in but the system still can’t see them. Not sure what to do next

To add John, when I plug the items back in they flash white for a minute then go solid white, not green suggesting they are restored to factory settings?

I hold the button in and then they flash orange, turn permanent orange but I still can’t see them on the app

No, removing power briefly simply reboots the item. Do not Factory Reset anything.

I’m sorry that I didn’t get to you sooner. It seems that you’ve at least attempted to Factory Reset. DO NOT FACTORY RESET ANY MORE UNITS.

Are there any SONOS units that have not been Factory Reset?

If this was a house, you’ve changed all the locks and left a pile of new keys on the kitchen counter -- while no one was home. It would be easy to pick up a new key -- if you could enter the house with your old key. 

With respect to the SONOS system, you have changed the WiFi setup, but SONOS needs to be able to use the old setup while it changes to the new WiFi setup. The keys are on the kitchen counter.

Sorted it.  Factory reset all devices and added them one by one.  There must be an easier way to change the password.  As soon as you change the password and open the app it loses the system therefore you can’t get into settings - system as it is greyed out

There is a simpler way. The WiFi password is a system level setting so should have needed at most a reboot of the other speakers. 

A huge difference between Sonos and other devices attached to your network is that there are multiple devices involved, with the controller on a different device from the system.