Did you already go out and purchase this wall plate? If you did not already buy it, then do NOT purchase that wall plate. Instead, purchase one like this one, as it has an HDMI socket on each side. No wiring. Of course, this still makes me wonder about why you only have one wall plate.
You should be using two wall sockets... the whole purpose of using wall sockets is for a professional installation, and if you are using only one, you kind of defeat that purpose.
But... you want wiring and pinout diagams...
..of course, you could just use two wall plates, and just be consistent between them. The reason why this is going to be difficult?
There is no standard for color-coding the wires and it can become very easy to make a mistake. I think it’s fair to say that you will have a tough time contacting the manufacturer to find the color code for the wiring.
But this article on repairing damaged HDMI cables might come in handy.
In the end... just getting wall plates that don't need to be wired might be the way to go.