You have to get in touch with TV manufacturer, Roku only supplies UI for Roku tv's. And Roku device remotes won't work on Roku tvs, they use a different IR commands.
Do you have old cable or directv remote laying around? They can be programmed for Roku tv's. Or any old universal remote, list the brand and model number I may be able to give you a code to control the Roku tv?
@lillarrabee30 If the older Roku remotes have a pairing button they can most likely be paired to your TV. However if they have no volume or power buttons they would not be able to turn on the TV or control the volume. Once paired you could use to access Netflix select shows etc. .
To add to @HDMIGuy suggestion of looking for a pairing button on the remote, also look for a little microphone button on the remote which would indicate a voice remote that you may be able to pair with your TV. However, with no power button on the remote you'd have to revert to the caveman way of turning the TV on and off.
I don't want to get your hopes up because it's more likely that none of your remotes for older Roku devices will be able to control your TV.
Without tv power button, this remote doesn't have tv IR on board. It may have voice search with magnifying glass or the backwards Q symbol on it. Anyways it only controlled the tv volume by hdmi-cec, not IR. With recent update the tv doesn't recognize it has cec device anymore. If you can't refresh cec devices in the tv settings, then try unplugging the power from both Roku and Tv a few times until the volume starts working again.