RBR20 how do I change the wifi channel for a device?

The WiFi channel for the 2.4G frequency band (which Arlo cameras use) can be set using the Orbi web interface.

Log in using the admin credentials ("admin" and the admin password, which is usually NOT the same as the WiFi password).

Navigate to the Wireless Settings and change the Drop Down menu from "Auto" to whichever channel you want.

I should point out that EVERY WiFi access point in your neighborhood scans the WiFi channel space from time to time and changes to whichever channel appears to be the least used.  So, just because Channel 1 appears to be the "best fit" right now, does not mean that it will be an hour from now.

Also, there is a bit of "folklore" in regard to WiFi channels.  Whoever designed WiFi YEARS ago created channels which "overlap".  There are only three channels (in the US and much of the world) that have NO overlap, 1, 6, and 11.  So, when a business deploys a number of access points, they take care to have adjacent access points not overlap.  (It's unfortunate there are not four non-overlapping channels, because it's a well-known math problem to determine how many colors are needed to have every country on a map be a color that does not touch another country with the same color.  The answer is four.  Sorry for the digression.)

This leads people to recommend, "set WiFi to 1, 6, or 11".  But, this does not take into account that your neighbor's access points may have settled on 2, 5, 7, or 11.

So, I doubt that changing WiFi channels will solve your problem, but if it does that's great.