I only run Plesk on CentOS, but there should be a similar directory on the Windows side. That being said, here's where I'd look - /usr/local/psa/admin/sbin. The filename I use is "ftpmng". Maybe search in the PSA directory for that. Here's what I get for help docs on that:
Usage: ftpmng [OPTIONS]...
--reconfigure-all
create configuration files for all domains
--reconfigure --vhost-name=<domain_name>
--set-disk-quota --vhost-name=<domain_name> --quota=<quota>
--get-disk-usage --vhost-name=<domain_name>
--update-user --user-name=<user_name>
--remove-user --user-name=<user_name>
--kill-proftpd-process --user-name=<user_name> --pid=<pid>
--features
returns PHP code which reflects state of several features support in ftpmng.
-h, --help
display this help and exit