Ask HN: Inherited the worst code and tech team I have ever seen. How to fix it?

I have to find a strategy to fix this development team without managing them directly. Here is an overview: - this code generates more than 20 million dollars a year of revenue - it runs on PHP - it has been developed for 12 years directly on production with no source control ( hello index-new_2021-test-john_v2.php ) - it doesn't use composer or any dependency management. It's all require_once. - it doesn't use any framework - the routing is managed exclusively as rewrites in NGInX ( the NGInX config is around 10,000 lines ) - no code has ever been deleted. Things are just added . I gather the reason for that is because it was developed on production directly and deleting things is too risky. - the database structure is the same mess, no migrations, etc... When adding a column, because of the volume of data, they add a new table with a join. - JS and CSS is the same. Multiple versions of jQuery fighting each other depending on which page you are or even on the same page.