Uh, did we just buy a new TV?
In the olden days, the carrier gave us a set-top box and that box outputs to channel 3/4 and that's where we tuned the TV to talk to this set-top box.
These days, set-top boxes don't talk to channel 3/4 but instead would have a connector, HDMI, COMPONENT, COMPOSITE VIDEO, where u hook up to a digital TV having one of these ports.
So with this new TV, channel 3/4 is no longer used but instead you tell TV to "connect" SELECT INPUT really where the set-top box is connected to, i.e. HDMI1.