Remember that Roku TVs use a different IR remote than the Roku players, so you can't simply get a "Roku Remote". There are generic IR remotes that have Roku TVs in their database, but you might need one that specifies Onn TV as well. If the TV has an Ethernet jack you could make a wired network connection and then use the Roku app on a phone or tablet. But if all you have is WiFi then you must have a working remote.
Roku does sell Roku TV remotes in their accessory store, and you might be able to find a new remote in places that sell electronics, such as a Walmart or such store.
https://www.roku.com/products/accessories/roku-tv-remote
Dan
Roku Community Streaming Expert
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