There are potentially three (3) places that affect the antenna vs cable source for the tv, but individual RV wiring varies.
One is a control switch for the Over-The-Air Antenna, basically on On/Off pushbutton on a wall plate somewhere. The external cable inlet coax may be routed through this switch, in which case it must be in the Off or Cable position for the park cable signal to reach the tv. The switch does two things: (a) selects whether roof antenna or park cable goes to the tv, and (b) tuns the roof antenna amplifier on/off.
The second is at the tv itself, where Cable or OTA (aka Air) is selected on the Settings menu. There may be multiple settings, e.g. source input jack, tuner type (digital, analog, cable, etc).
The third possibility is a separate tv source switching box, which may allow choices of different sources such as Antenna, Cable, DVD, Satellite, etc. These aren't as common as they used to be because most newer tvs have source switching built into the tv.