How do I convert a cargo aircraft livery to a passenger aircraft livery?

Hey pilots!

So, recently I wanted to update the livery of my Headwind A330-900 to the modern Avianca livery, unfortunately, Im not very good at graphic design, and there was none available on flightsim.to, So i went and got a cargo livery that was in the modern style and took to modifying it, the wounds of hours of booting up and shutting down MSFS are still fresh so im not gonna delve into them right here, but, i've fixed everything else, just one problem...no windows

Now, im not smart enough to fix this problem, im nearly convinced its some sort of config problem, but I just cant find the way to change it

Nearly finished A330-900 sitting on the ground at 'El Dorado' intl airport

Does anyone here have any livery experience? and if such do you know what causes MSFS to render an aircraft with windows for the passengers? sorry if this post is a bit out of character for this subreddit but i just cant think of any other way to get an answer

thanks pilots!