You can delete all of your references at once by using the master checkbox, but please be aware, this action cannot be undone – if you permanently delete references, they can't be recovered.
How to delete references in bulk?
just make sure you're in the All references section, then click the little arrow to the right of the master checkbox as shown:
You'll then see the option to select all references:
Once they're selected, you can delete them all using the trash can icon.