Pivotal does not recommend that you edit the configuration which is generated by the build pack. The PHP buildpack should generate all configuration required to deploy your app. If you are manually adjusting the HTTPD configuration, that's considered an advance customization and you would need to be familiar with editing the HTTPD configuration to do that. Pivotal does not provide or recommend a UI to edit this configuration.
That said, if you have a tool that you like there's nothing stopping you from copying the configuration that is generated out of your application container and editing it, or using your tool to edit the default HTTPD config files that are shipped with the buildpack.
https://github.com/cloudfoundry/php-buildpack/tree/master/defaults/config/httpd/
Hope that helps!