This happens to me all the time when I misspell someone's name, or I call a guy Uncle Sam in one and Sam Spade in another, so I get two albums of the same guy.
In People in Ventura, you can just drag one person's album into another, and Photos will ask, "Is this the same person?" If you say yes, then they will combine into just one album. If you don't like the name, you can type in a new one.
I'm not sure if this worked that way before Ventura-- I remember clicking on one picture, command-clicking on another, and right clicking to get a menu. The menu included "merge 2 people." This still works in Ventura, as well.