I've never used the Spectrum channel, so this is just basic guidance.
- See if there's somewhere within the channel to log out of the account. If you can log out, you should be able to log in with your new information.
- If that doesn't work, remove the channel from your Roku. Press the * button while the tile is highlighted on the home screen and select Remove. Once that is complete, you must reboot the Roku. Pull the power if you can't find system restart in the menu. Then install the channel and enter your new user information.
- If the removal didn't change the user account in the channel, then a factory reset might be necessary. Sometimes those channels simply don't clean out like they should.
Even if you had contacted a Roku support person, they simply would have advised you to contact Spectrum for support. Roku does not create or provide support for 3rd party channels. Spectrum is responsible for the functionality of their channel, and would be the only ones that can assist you with the app.
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee, just another user.