To use the command line scripts, you will need to connect to your server via SSH or another terminal shell method.
HTML files are located on a per-domain basis under /home/user/web/domain.tld/public_html (replace user and domain.tld with the respective user name and domain name).
Currently we don’t support adding or removing features after Hestia has been installed, so in this case would recommend to reinstall from a fresh OS installation and ensure that you specify the correct flags during installation – you can use the tool here (https://gabizz.github.io/hestiacp-scriptline-generator/) to generate the necessary command line to install the features you need. This is something we’re working to improve in future releases, and starting with v1.1.0 we have added support for adding/removing PHP versions with the MultiPHP system for example.
Hope that helps, let us know if you have any other questions.