Currently, the options on Service Management HelpCenter customization options do not include editing of home page layout. This option is available on cloud editions as explained in the documentation https://support.atlassian.com/jira-service-management-cloud/docs/edit-the-home-page-layout-in-your-help-center/.

Along with other features, it allows sorting of available portals and make a particular one prominent if the users are have access to more than one portal.