Sorry but no. If your old roku tv remote was from tcl, insignia, haier, hitachi, philips, jvc, magnavox, westinghouse, sanyo, or element then it would work with your Onn roku tv. But the roku tv remote from Hisense or sharp do not work. Or though your onn remote would probably work with hisense Roku tv itself even though the reverse wouldn't.
Go to walmart get a true roku wifi voice remote, it work with all brands of roku tv once they are paired. Or you get the One-For-All urc-7935 streamer universal remote for about $16.88, heres photo next to roku tv wifi voice remote: