If you forgot the email used for signing in, it can be checked via the set-top box. Go to the settings: Settings → System → About.
After signing in, follow the link in a web browser: https://owner.roku.com/channels/detail/5JNHJL5. Click – Add channel
Go Settings → System → System Update on the Roku set-top box and click Check Now. Then Player will be installed on the Roku set-top box.