@Bod1 if you can connect your Roku to your network with an Ethernet cable, then it's possible you could use the Roku app on a phone to control the Roku. If you cannot use a wired network connection, then you must have a Roku-capable remote. Since the old Roku 3 is capable of using an IR remote, you can find very inexpensive generic IR remote that can be used (just make sure it lists Roku players as supported devices).
However, I have to point out that the Roku 3 is extremely old (there's two versions, one released in Mar 2013 the other Apr 2015), and while both versions are still supported by Roku there are some service providers that will not permit their service on these players. For $18 you can get a brand new Roku Express that will work with all providers, as well as getting a new remote with it. Or for $25 you can get the Roku Express 4K+, which comes with a voice remote that doesn't require line of sight to use, as well as 4K/HDR support and much more memory for both the system and channel storage.
Dan
Roku Community Streaming Expert
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