How to change Plesk Server Default page
Default pages are located in the HTTPD_VHOSTS_D/default/htdocs (non-SSL) and HTTPD_VHOSTS_D/default/httpsdocs (SSL) folders respectively. You can replace them with your own ones if needed.
HTTPD_VHOSTS_D is a variable that specifies a path to virtual hosts’ locations and may vary depending on the operating system and Plesk version.
This path is defined in the /etc/psa/psa.conf configuration file.