If you don’t understand how plumbing works it’s still ok to try to fix the plumbing at house you own. You might make it worse but it’s yours to break.
On the other and, if you don’t know how plumbing works don’t sell your services as a plumber. It’s misleading and unfair.
There are many people out there pretending to be something they’re not. I’m not talking about fake credentials but rather presuming to have an expertise they really don’t have.
If you don’t know, don’t do until you have learned. Also, if you don’t know, don’t charge as if you do.
Just something to think about.
Have a great day!