Adding 'subscriber' listings as an Admin

I’ve set up the Directory so that a member of the public can sign up (as a Subscriber) and I have given the Subscriber role the permissions (via User Role Editor) to create and publish listings.

However, there will be times when I, as an ADMIN, need to add a listing on their behalf.

However when I go to add a listing, where it says Author, it doesn’t allow me to select the user (subscriber) to assign that listing to them.

How do I do this please?