If you've forgotten your Hide Backend URL you can find the new slug via FTP in your .htaccess file. You may have to adjust your FTP client to show hidden files. Look for the for the code block that resembles the one below. Notice "wplogin", this will be your new login URL.
# BEGIN Hide Backend
# Rules to hide the dashboard
RewriteRule ^/site/wplogin/?$ /wp-login.php [QSA,L]
# END Hide Backend