I am the foremost authority on absolutely nothing and it works well for me. Like most people, I know a little about a lot of things, but am no expert in any of them. I taught myself how to do what was needed for my job, such as learning Windows 98 when it first came out. (Yes, I’m that old.) I also taught myself how to do a website and ended up the webmaster for a large healthcare system. Before that I was grandfathered-in (no formal education) as a licensed social worker at a nursing home. Loved that job.
When I did go to college in my fifties, I got a bachelors degree, but couldn’t tell you what I learned because I didn’t retain any of it and I’ve never needed to use it. But, by golly, that diploma is framed and hanging proudly on my office wall. Unfortunately, I’ll be paying off my student loan long after I’m dead.
Anyway, my point is, you don’t have to be an expert as an author (non-fiction authors might be excluded). It does require a love of writing and tons of research, though. Find a supportive beta reader (hi, Joyce), hire a good editor and write to your hearts content.