Add script to WordPress menu bar

I am using Vantage Premium theme and would like to use Appointlet’s script (pop-up) and add it to the nav bar as a link. I would want to add this:

<a href="#" data-appointlet="APPOINTLET_APP_NAME">Schedule an Appointment</a>
<script>(function(e,t,n,r){if(e)return;t._appt=true;var i=n.createElement(r),s=n.getElementsByTagName(r)[0];i.async=true;i.src='//dje0x8zlxc38k.cloudfront.net/loaders/s-min.js';s.parentNode.insertBefore(i,s)})(window._appt,window,document,"script")</script>

I have tried to use Easy Modal plug-in, CSS Classes option and attempted child themes but I’m probably just not doing this right. Can someone help?