Does the remote have a microphone key or crescent moon? The one with Microphone means its wifi remote and has to be paired with the tv. The one with Crescent moon is an IR remote should just work without the need of programming. If it an IR remote check to see if it working by looking at it through cellphone camera, if you see a flash as you press a key its working, no flash its not working and has to be replaced.
Please contact your TV's manufacturer directly to report this issue and request additional support. Each Roku TV manufacturer provides direct support and warranty services for their products running the Roku OS.
If you need a replacement remote for a Roku TV, you would need to contact your TV manufacturer. You can contact Hisense here: https://www.hisense-usa.com/support/ or at 1-888-935-8880.