Your current Bravo account is tied to your former ATT provider account. You need to change this.
I don't have Bravo channel to check details but ...
Somewhere in the Bravo channel app you should be able to find an option to log/sign out of the current Bravo account. It could be under Settings, Options, Account, or something similar. Once logged/signed out, you should then be able to log/sign back in using your current account provider credentials.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X