That’s something you’ll need to go into the service menu to fix. Do you have the original remote for the TV? You’ll need that (usually) and the service menu code (can lookup online) to get to where you can adjust it.
Sometimes you can also sort of adjust GPU scaling in your GPU settings, though that’s heavily dependant on your setup. I only have over/under scan options on mine but I don’t know how Nvidia’s control panel works.
You should try to run something at 480i next. I’m very curious to see if you have the same jittery interlaced problem I’m having with this adapter.