The TV I inherited has another Roku account already programmed from the person who used the TV before. So I cannot switch to my ROKU account to watch what is allowed under my RokuTV account email address and pin and password
You will just have to Factory Reset this inherited RokuTV and then setup/activate using the same Roku account (email address) as your current RokuTV. This procedure will link both RokuTVs to the same account.
Roku devices are linked to a Roku account during setup and activation of the Roku device. You cannot simply transfer a Roku device to an existing Roku account.
To Factory Reset your RokuTV, you can find the Reset button (usually a pinhole) and press and hold for 30 seconds, or you can go to Settings/System/Advanced System Settings/Factory Reset.
If you happen to know the Roku account info of the inherited RokuTV, not a bad idea to login to the Roku account and make sure all subscriptions are cancelled and "Deactivate" the old/unneeded Roku account.
Roku Community Streaming Expert Just another Roku user... I am not a Roku employee. Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102