When I tap Photos|Search on my iPhone XR (running iOS 12.4), I get links to "Categories" of images. Clearly a program has assigned categories to some of my photographs. For example I have three photos of a stretch of coastline, and these have been assigned the category "Cliffs".
How can I get control over these categories, by which I mean how can I create them, delete them, rename them, and assign and unassign images to them?
I do not use cloud services.