Yell

Sign in from Yell.com
Click on profile, then Edit Profile.
Click on Manage your Website, then Manage Website.

Adding GTM to the Site

Using the on-site builder, click on Settings, then Head HTML.
Add Tag Manager to the 2 sections of the site & save it.

Adding Form Tracking

Using the on-site builder, find & click on the Contact Form.
Click on Submission, then Tracking & add the below tracking code:

<script>
var dataLayer = window.dataLayer || [];
dataLayer.push({'event' : 'contact-form-submitted'});
</script>

When done don't forget to Republish your changes!