The plugin used in this tutorial is jQuery UI widget.
You can download from repository directly or from the following link

Download Plugin

Following code will go into integration section;
Divi > Integration > Above Head

<script type="text/javascript" src=""></script>

Following code will go into jQuesy script;
Dashboard > Settings > Jquery UI widget

jQuery(document).ready(function($) {
$.scrollify({ section : ".et_pb_section", });