How do you find a professional editor?

Reedsy is a good starting place.

Search profiles, read their bios, make sure they work in your genre. When you find one you like, send them a sample of your work.

If they agree to work with you, your very next question should be, "Can I get a sample of your work?" If they say no, run like a giant bear is chasing you in the opposite direction.

When they say yes, they either edit the sample they already have or you send them more. If they understand your vision, your voice, and you like the suggestions they make, congrats, you've found your editor.

It's okay to be picky. In fact, be picky!