My advice these days is to avoid the migrate/convert rabbit hole and start over rather than trying to climb the ladder, which, if you're not already tooled up, will likely be more work and still require manual labor to your swift along the way.
Also, pls. resist duplicating your question in different threads, thanks.
KMT.. You didn't provide any useful information and then gave pointless condesending advice.. Don't do that.
Some people have larger projects, so rather than "rewritting everything" it would be smarter/faster to just re-image your Mac to an older version that supports Xcode 9 and then do the migration, save your updated repo, and then re-image your Mac back to Catalina.