The best way to fix the issue on you local server is to create a new template file with your changes.
How ever if all the current templates file are affected please create a issue report with all the detailed information / changes that need to be made or if you now how Git works please create a pull request. In that case we can review the changes and release it with the next update.
The default template files can be found in https://github.com/hestiacp/hestiacp/tree/main/install/deb/templates/web/nginx/php-fpm
or https://github.com/hestiacp/hestiacp/issues.
All the help is really appreciated how ever it can take some time before pull requests are accepted.