You didnt mention your Roku model #.
If you have an Ultra, you use the Remote Finder functionality (button on the Ultra).
If you dont have an Ultra, and if you look hard and you dont find it, buy a replacement remote.
You can get an IR-only Roku-compatible Universal remote (not for stick models) at Walmart/Best Buy/etc for $5-15.
You can get an official $20 Voice Remote (RCAL7R) or $30 Voice Remote Pro (RCS01R) at the same or from Roku.com.
I read something about a ping used to locate the remote. Don’t know how to initiate it
Re-read above post, especially re:Ultra vs non-Ultra.