Check out this thread:
https://forum.xojo.com/t/has-anyone-used-ai-specifically-to-convert-api1-desktop-apps-to-api2
I recently learned that the latest Xojo will load and compile projects that still use the old classes - Window instead of DesktopWindow, Listbox instead of DesktopListbox, etc. So a reasonable first step I think is to do that and get your app to compile and run before attempting to update to the new classes. Apparently a project can even include old and new classes, although obviously not in the same window.