If you like to create a clone of a WordPress staging site which you’ve created earlier with WP Staging you need to change something first in the database.
Open your favourite database administration tool like phpmyadmin or the one file solution adminer.
Look for the entry
wpstg_is_staging_site in the table
option_value to false or remove that entry at all.
After doing that you are able to clone the staging site as usual by going to your WordPress staging site > WP Staging > Sites