I had a guy put in a new SSD and 8 more GBs memory, but he brought it back with Catalina installed, and a dump of my old folders/files on the desktop. Since my employer only uses Mojave, I called the guy and he told me to downgrade, which I did. But I still have two or more main drives. One is called Untitled and the other Untitled-Data. The untitled-data drive is home to mojave now. The other drive is mostly empty.
I'd like to return to having one drive with all my stuff on it. I seem to have another drive (?) with my name on it as well as the two untitleds.