Remove an unassigned face, without removing the picture

[vbelloir]

Hi folks,
I'm using recognize with memories as UI
Before definitely adoping it, I'm playing this a test collection, with very old scanned pictures.
There is a lot of unassigned face, which is quite normal with only one occurrence.
I don't want to create a cluster with that face, I only want recognize to forget it, without removing the picture.

How can I achieve that?

Thanks.
Vincent