@Grendal
During setup and activation of any Roku device or RokuTV, just use the same email address as any prior Roku device and that will "link" all Roku devices to that account.
You can see the email address that your Roku account is registered under through Settings/System/About on your Roku devices.
https://support.roku.com/article/360000321787
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