Only he can fix them.
Well, you could with Airport Design Editor tool by having it create a project for you from the airport and you can edit it and recompile the package and so on and so forth, but, that’s a lot of work and learning.
If you find a problem in dev mode, take a picture and message him.
People make mistakes, and, it’s very easy to think to taxi sections are connected but they aren’t. So, if the path to the runway isn’t complete (IOW, if there’s a break somewhere, or the hold shorts are broken, or not attached to the path), no plane can leave the parking spots.
Asobo has been “improving” their error checking… I’ve found issues with my airports that appeared because of apparent changes in the way Asobo processed taxiways. I know they were connected before, but, for some reason, Scenery Editor worked differently somehow and they no longer were connected and I had to fix them.