Been there. Done that. I have a thread on here somewhere talking about it but I'm on my phone so searching isn't that easy.
And I didn't look at what trailer you have before I started typing and on the phone I can't glance back so I'm assuming it's similar to my trailer.
But to summarize it you need to access it from the side. I pulled the head unit out so I could shine a flashlight back in there to see. But you can pull the upper panel above the DVD player. You have to unscrew it and unscrew the plug so you can release the panel.
It's quite difficult to find everything because you can't see so you're working on touch.
I really recommend you pulling the HDMI splitter out of that compartment and move it to under the DVD player. The HDMI cables are very stiff so they will continually pull out while bouncing around. Go and secure the splitter under the DVD player. Plus HDMI splitters are none to go bad so expect to have to replace it eventually. So moving it will make it easier to replace.