Somewhere on that device should be actual buttons. They may be behind a panel, underneath the screen, on the side, farther back on the side, or in any number of places. You'd need to see the TV manufacturer information about that. Roku doesn't build Roku TVs. Roku supplies the software interface, but not the actual hardware.
DBDukes Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution." Note: I am not a Roku employee.