Welcome to the Roku Community!
We understand that you are inquiring about changing the Roku account email address on your Roku device, is that correct?
If your Roku device is already linked to a different Roku account, we recommend performing a factory reset and re-do the activation process.
For more information about how to factory your Roku device, visit our Support page here: How to system restart or factory reset your Roku streaming device | Official Roku Support
Then link your Roku account to the Roku device, You may also refer to this link: How to activate or link your Roku® streaming device | Official Roku Support
If you need further assistance, feel free to contact Roku support at https://support.roku.com/contactus