Add Pre Roll Video on Youtube Iframe

Question

i've this type of code made in wordpress + jnews theme:

<div class="jeg_featured_video_wrapper"><div data-src="https://www.youtube.com/watch?v=ID-VIDEO" data-type="youtube" data-repeat="false" data-autoplay="false" class="youtube-class clearfix">
                    <div class="jeg_video_container"><iframe width="700" height="500" src="//www.youtube.com/embed/ID-VIDEO?showinfo=0&amp;theme=light&amp;autohide=1&amp;rel=0&amp;wmode=opaque" frameborder="0" allowfullscreen=""></iframe></div>
                </div><div class="floating_close"></div></div>

i want to display my ad pre roll taking them from my google ad manager account (i've this vast tag https://pubads.g.doubleclick.net/gampad/ads?iu=/21753730968/test_video2&description_url=https%3A%2F%2Fsite.it&tfcd=0&npa=0&sz=400x300%7C640x480&gdfp_req=1&output=vast&env=vp&unviewed_position_start=1&impl=s&correlator=

how to do this?Thanks

I tried also to insert the code that is taken from https://ytvastqa.appspot.com/ but nothing happens.