Tracking referral path

I have an embedded booking site within my website. The booking site provides a Google Analytics Ad-on. However all conversions on Google Analytics are showing as Direct traffic and referral path not set.

I have checked what’s happening on real time analytics. It would appear that as soon as the customer goes to the embedded booking site the referral path is lost.

My booking site provider advises the following:

The modern universal analytics script doesn’t require any special configuration to track this data through the frame, but the interface script that connects the sites does need to be able to access the script from the standard names Google defines. The Yoast plugin unfortunately appears to be renaming ‘ga’ to ‘__gaTracker’ on your site, which would prevent it from being accessed by the standard name. I don’t know if it allows configuring this back to the standard value, but if you can change it to the standard ‘ga’, that would likely fix it.

If you can’t change it, you could always add the script into a header file manually — an example of this from another account is:

<script type="text/javascript">
  (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
  })(window,document,'script','//www.google-analytics.com/analytics.js','ga');
  ga('create', 'UA-46363502-1', 'auto');
  ga('send', 'pageview');
</script>

This is all a bit complicated for me. I need someone to literally walk me through the steps I need to do to fix this problem. If I upgrade to Google Analytics by Yoast Premium is this the sort of thing I could get help with? I have extremely limited knowledge on coding.

http://www.totsontour.co.nz

https://wordpress.org/plugins/google-analytics-for-wordpress/