2 mixed up faces in Photos - how to "unlearn" one?

I have by accident confirmed a wrong person's face (person B) to another person's collection (person A). Now a half of the photos are of person A and another half of B. They are not at all similar (a man and a woman).

Now, I know the "This is not XY" feature where you can select a face on a specific photo to remove it from a collection. But I have literally hundreds of photos of the wrong person B now in the person's A collection. I tried to remove two dozens of them like that, selecting multiple and choosing "These are not person A" but it doesn't remove other of person B.

Is there a way to fully remove, ie "unlearn" a person's face from the people collections and start learning them from scratch again? Or do I have to spend hours manually untagging all the wrong photos of person B in persons A collection?

I tried to Remove this person on person A but it only hides it from the People collections, the face stays recognized in photos.

Please help! Thx Martin