Change network on Sonos One

@Afa2222

Within Sonos app go to system settings and manage your network settings. 
https://support.sonos.com/en-us/article/connect-sonos-to-a-new-router-or-wi-fi-network

If it’s a Gen 1 Sonos One then I believe you need to factory reset the speaker. Before you do that, is it your only speaker or do you have other Sonos units that you have managed to successfully reconfigure for your new WiFi? 

I have tried to reset. Its my only one

Did it get to a green flashing light on the speaker before you tried to add from the app? 

yes

I guess the only thing left to try is to delete the app and its data, and re-install the app. 

If that doesn’t work then I’d get in contact with Sonos Support who may be able to help more. 

Thank you! I will try that

Btw… would be interesting what in detail you have changed on your network. Maybe there something is causing the issue. 

And just to add… the suport article I linked above also describes the procedure for S1 (just scroll down). 
A gactory reset always should be ultima ratio, in special if you just use one device and all system data will be lost. 
 

Edit: 

And one more question… can you exclude that the One by mistake (maybe by experimenting with S2 app) got an update to S2 firmware?

I got installed an all new internet. Different box and type of network. I think I have updated everything

So as there nothing could become more bad I would start like doing a complete new setup. Speaker seems to be reset already… Reinstall the app and select „new system“. Log in to your Sonos account and start adding the speaker as the first room. 
Everything else like adding music services, adjusting sound, adding voice assistant etc. can be done after that.