The Roku Voice Remote only works with Roku devices, not your Samsung TV. Even if Samsung had a voice remote I couldn't say if it would work with the Roku app. Your best bet is getting a Roku device that comes with a voice remote if you really want that feature.
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee.