I assume you have scrolled through the input options for the various choices to find which one your TV audio output is connected to. I can't look at our unit right now, but I think there is a separate audio cable that connects TV audio output to the amplifier on one of the input ports. If you put a DVD in the player, it should automatically turn your TV input to the DVD player and start right up so you can see the movie, and you should get sound through your speakers. If you don't see any audio cables connected to both the TV and Amplifier, that may be your issue. Usually they ship with an extra pair, mine was connected and had a spare set as well. You may need to remove the unit to get to the connections. To do that, you have to remove the top and bottom cover trim to get to the four screws that hold the unit in place. It can be tricky to get that trim piece off, the after that, it's easy to access everything.
While you are at it, check to be sure your speakers are wired correctly. Many of us discovered the speakers were all wired to just the left or right channel. You'll notice that if you listen to a CD with good stereo separation.
2020 Eagle HT 30.5 CKTS Modern Farmhouse (16" wheels, spring shackles set on lower hole of frame, SumoSprings TSS-107-40, standard kingpin, B&W Companion slider, TST-507 TPMS)
2019 F250 SRW SuperCab 4X4 SB 6.2 (10,000# GVW) 3.73 Axle 18" wheels