The step-by-step: https://standardebooks.org/contribute/producing-an-ebook-ste...
In a nutshell: start with a Project Gutenberg text, clean it up to a high standard, have it peer reviewed and published
However, I was completely shot down by the local library when I was discussing it with them. They said they already had a photo copy and didn’t need anymore digital editions, I tried to explain the benefits of having it in a machine readable format but they wouldn’t entertain it. I completed the project for me, so I wasn’t too bothered, but thought they might have been interested in archiving it but they weren’t.
My general feeling is that they didn’t like an outsider contributing and touching on a format they didn’t know so got slightly defensive.
Beyond that, if the material is public domain, that library is called The Internet. Post it and promote it. The only reason to seek association with a library is if you're looking for cred for some reason, and that's not the business they're in.
If it's not public domain, or if you haven't marked your derivative work public domain, then you put a library in an awkward position. Realize that these are the types of people who still post little notes by the copy machines saying what's permissible and enjoy policing it.
Most just say no for the same reason that Hollywood returns ideas and scripts unopened. They're busy and the cost/benefit isn't there.
Although the self-described online ones tend to play fast and loose, real librarians have a formal code of ethics which is worth reviewing.
In my case I picked a title from the project’s wishlist and almost started but searching the mailing list showed that someone has just started. I found another title by the same author: https://groups.google.com/g/standardebooks/c/IP0emhSQ6Bw/m/B...