that's what i saying too
when stuff still plugged in via coax on older systems, the tv often had to be set to a specific channel (usually 3 or 4) to see the cable box feed. then the channel was changed on the box and not the tv. it seems like this is what the question is asking. how to do this with the new tv. but that style of input is not used anymore since tv's have a range of options including hdmi, pc inputs, usb, composites and so on. the source is changed through the tv menu now or through the remote.
my suggestion is that his tv may have the option to hid the inputs not being used so when he pushes the source/input button, it only goes to the ones actually being used which is how i am reading the question. some tv's also allow you to rename the inputs so if you can't hide them you can at least easily stop at the right one labeled "cable" or "xbox" or whatever.