Tagging or adding a person/name directly from photo

I want to be able to tag a new photo with an existing person in my People list or be able to add a person to my People list directly from the new photo in Lightroom.  Currently, I can only add a name in the right-hand panel if Lightroom detects unrecognized people. But sometimes it doesn’t even allow me to add a name, even though there are new people in the photo.