How can I have the photos updated in the 'People' section on Photos App?

The “main” photo for a person in the “people” section of photos can’t be updated that I can find. The main photo of me was a really bad and irritating photo of me. After a long time of hating it, I went back to delete the original occurrence of the photo and thought it would update to another random photo of my face. However it has not done this and it is now just blank which is so weird. How can this be chosen or edited???

[Re-Titled by Moderator]