Roku voice remote has not controlling power and volume for NIKAI UHD 55 inch Tv . How to solve this?

Warmest welcome here in the Roku Community, Mahmood!

We'd be more than happy to assist you with your remote concerns.

Before proceeding, may we know what Roku streaming player you have connected to your Nikai UHD TV? Also, are the Power and volume buttons only affected by this? 

Looking forward to your response so we may be able to provide you with an accurate resolution. 

Best regards,
Carly