Resize/move video position on 8" picade screen?

I hooked up my 8" Picade screen to the output from my Retrotink 2x mini because I had the idea of using this setup for an N64 handheld. However the image from the N64 isn’t in the center of the screen and looks a bit squished. I can’t seem to use the screens built-in settings to change this, because the second menu option which I think this kind of setting might be accessed under isn’t available.

Is there any way to access that option or maybe some other way of making such settings? Maybe a firmware flash?