How to get rid of the black bars, completely stretching the screen on Citra?

I recently found out it’s possible to stretch the “main” screen of Citra through this youtube video… I don’t know if I am allowed to post a link to it, so I will paste just the code: watch?v=80E_mo-ZvyU

The game is Dragon Quest 7, the author somehow stretched the main screen all the way, but still keeping the secondary screen at the lower right corner. Can you people teach me how to do this on PC? I have a 4k monitor… and I am aware we can configure the qt-config.ini file, but I followed some tutorials and none of them worked, it seems the author used hex codes to “hack” Dragon Quest 7 and that allowed the screen to stretch even further?