It’s hard to understand what you want to do.
Do you want an actual duplication, where it has the same Parent Class as the original one? Then you should be able to just rightclick it and hit “Duplicate”.
If the ParentClass accidentally goes “missing”, you can open the new BP and got to the top left EDIT button and hit “Reparent Blueprint”. There you can
choose the correct ParentClass again.
OR
Do you want the PlayerClass as a Parent Class for another Blueprint? Then you can do what @PhoTek told you (: