unfortunately i think it might be saved in my sonos account and i dont know how to clear it out.
If you’ve removed Spotify from the Sonos app, your account details will also be removed.
After testing on my system, Sonos will automatically authorize Spotify if you’re signed into it on the same device. You can tell it’ll do this if you see Spotify under “Suggested Services” in Content Services → Add Content Service. It’s most likely you’re still signed in somewhere, either in the Spotify app itself, on your phone's web browser, or in a password manage on your phone (my Samsung phone has one built-in).
What you can try, is to remove the Spotify app from your device with the Sonos app then try to add Spotify to your system, this way it’ll ask you to authorize via login details instead of authorizing for you.