If its a true Roku tv IR remote then it will just work without you having to pair it. If its not working then you might have the wrong remote.
If you don't have a roku tv and are just wanting stand alone roku IR remote to control your non-roku tv, it can't, only Roku wifi remotes have tv controls.
So what kind of roku do you have? what is its model name and number? Describe your remote? Does it have tv power key and volume keys? Does it have crescent moon key?