How do I assign a property to a user/owner/lead?

You can assign or re-assign a listing to a user or owner from the property page. You can also create a new owner for that specific listing on the spot.

Or, from the property list, select the listing(s) and click on the bulk action button and choose Assign To, and pick a user/owner/lead and confirm on the change. You can also create a new lead for that specific listing on the spot.