If you have the Simple Remote, there are no TV controls on that remote. (power and volume).
The Roku Voice Remote has a TV Power button and volume controls on the side of the remote. (up, down, mute).
If you have a Roku Express 3900 or newer, or the Roku Express 4k that came with a Simple Remote, then you can upgrade/purchase a Voice Remote and have power and volume control for your TV. Otherwise, will have to use your regular TV remote (one that came with your TV) to control these functions.
Walmart, Best Buy, Target, Amazon etc all carry the Voice Remote as well as Roku website. (about $20)