If I remember correctly, when you’re in the Foxpro Programming Utility there’s a channel selection tab or button where you can change the caller channel. Then under the settings menu on the remote you have to change the channel on the remote to match the caller. Doesn’t need to go back to FP.
At least that’s how it is for the Fusion and X2s callers, and I would guess any that use the TX1000 remote. Not sure about some others.