You will find video background in index-video.html file. For banner video background the code is give below
<section class="hero-area-video" data-vide-bg="video/office.mp4" data-vide-options="loop: true, muted: false, position: 0% 0%">
<div class="dark-bg"></div>
<div class="block">
<h1>Word,Design,Development</h1>
<p>Most easy 3 keysteps for our agency</p>
<a href="" class="btn btn-main">Explore More</a>
</div>
</section>
video file for background is located in video folder.
Change the data-vide-bg url for change the background.
And Change contents from block class.