Lost tv remote need phone to turn on tv
All TVs I've ever seen have a button on them somewhere (usually on an edge or the back) to turn them on.
You didnt mention your Roku/Roku TV model # and firmware version: Settings/System/About
If you want a replacement remote:
The $20 Voice Remote (RCAL7R) or $20 Voice Remote Pro (RCS01R) available at Walmart/Best Buy/Amazon/etc or from https://www.roku.com/products/accessories should work.
Otherwise, you can download the Roku Remote app to control your Roku/Roku TV (assuming they are both connected to the same network).
All TVs I've ever seen have a button on them somewhere (usually on an edge or the back) to turn them on.