I want to use
If you're asking for a file in place of 'index.html', see "DirectoryIndex" to tell it what files to use in place of 'index.html':
DirectoryIndex about.php index.html Options –Indexes
... if you're trying to redirect all directories to a single page, then I'd cheat and do the following, which will mostly do what you're asking for:
Options +Indexes IndexOptions +SuppressHTMLPreamble IndexIgnore * HeaderName /includes/header.html ReadmeName /includes/readme.html
... and set /includes/header.html with whatever message you want (or containing a meta-redirect), and /includes/readme.html to be blank.