Face Recognition of Faces With The "Unknown" Tag

Dear Digikam-Team,

I have some 11k photos in the "People > Unknown" ¨category".

I want to restart a face recognition just on these photos since I've done quite some manual 'training' of the face recognition
in several albums by manual assigning tags to photos. And many people in the "Unknown" category are in the database now.
I think it would be a good idea to have a re-run just on thiese photos.

But I did not find a way to start the face recognition just for the
photos in "Unknown".

I really appreciate your advice on getting this  done.

Thank you in advance and best regards
Axel