Apple TV does not offer a login for Paramount Plus. It only offers to let me subscribe.

To access Paramount+ with a Paramount+ subscription as started outside the Apple TV app, you will need to use the separate Paramount+ app. You may install individual apps on Apple TV box (4th generation or later) from the on-device App Store.

Identify your Apple TV model - Apple Support

Paramount+ app - App Store preview - Apple

everytime we try to login to Paramount + using the app on the apple TV we got in partnership with Spectrum, it give us the option to subscribe....don't want a second subscription from apple just to use the one we have with the content provider.

Please advise how we work around this or is this a locked device like getting phones from att?

There is no work around, contact Paramount for assistance, this has nothing to do with Apple.