Plesk is control panel server software, similar to Webmin.

Login does not work on Chromium on Linux. Use Firefox.

Plesk accesses a lot of ports when running. It may be simpler to disable the firewall while working with it.

Howto Change Admin Password

Password should be from 5 to 16 symbols and should not contain login name, whitespace, quotes or national characters.

cd /usr/local/psa/admin/bin/
export PSA_PASSWORD="newpass"

This will take a few seconds to run. Afterwards, the password is available in /etc/psa/.psa_shadow