you piggybacked one through another. whatever you turned on would interrupt the signal and output the system in question.
I think I had 4 RF tuners daisy chained at one point for Atari 2600, NES, SNES, and Genesis.
Two consoles wasn't really a thing back then. If you had a Nintendo you weren't really messing with anything older anymore. At least in my experience. If you wanted to switch you just changed the plugs around.
I knew some kids privileged enough to have both a SNES and a Genesis.
It wasn't impossible.
Also VCRs used the same RF switching system.
The real question was, why would you have more than one of these things on at any given time?