This is the normal procedure for scanning for OTA channels in a new TV. Connect the antenna via the coaxial cable, make sure the power supply for the antenna is on. Turn on the TV. Click on the INPUT button and select Antenna. Click on menu and find the scan program and click on scan. If no scan, the antenna isn't good.
I'm can only guess that you have a BOMB, you didn't say, so a coax cable from the antenna should be moved to the Antenna In connector, connect the park cable to the Cable In connector and a install a short coax from the Signal Out connector to the signal in on the back of the set. Push the appropriate buttons on the BOMB to have either the cable or the antenna feeding the TV.
As stated before, bypass the BOMB, do not worry about the HDMI cable that is for hooking up the DVD player or if you have it the BluRay DVD player.
There are about 924 thousand schematic diagrams on how to hook up a TV in a motor home you can look at by doing a search. A couple of photographs or clear and concise descriptions of what equipment you have on board would help. We know you have a player of some type, I would guess a DVD player because you have movies going and we know you have an antenna but we don't know about a BOMB. There has to be something that directs either the Antenna or the Park Cable to the set either a BOMB or a A-B switch.
Selecting the correct input is a key factor in getting a signal in.
"I travel not to go anywhere, but to go. I travel for travel's sake. The great affair is to go". R. L. Stevenson
David Bishop
2002 Winnebago Adventurer 32V
2009 GMC Canyon
Roadmaster 5000
BrakeBuddy Classic II