[WP] GTM data layer push for Gravity Forms

wp_gtm_data_layer_gravity_forms.php

<?
  /**
  * GTM data layer push for gravity forms contact form
  */
     /**
      * Pushes a submission variables to the GTM dataLayer
      * Also pushes the event label for use in GTM tracking
      * @param  Array $entry the data submitted with the form
      * @param  Array $form  Form data
      * @return null
      */
     function gf_gtm_tracking($entry, $form) {
       //FORM IDS:
       // 4 = contact, 5 = venue inquiry
       // array of form IDs we care about tracking
       $form_ids = array(4, 5);
       //if the form ID isn't one of the ones we have specified
       //return without doing anything
       if(!in_array($form['id'], $form_ids)) return;
       switch ($form['id']) {
           case '4': ?>
               <script type="text/javascript">
                   jQuery(document).ready(function($) {
                     // var eventLabel = $('#event_label').val();
                     window.dataLayer = window.dataLayer || [];
                     window.dataLayer.push({
                       'event' : 'formSubmissionSuccess',
                       'formId' : 'bookThisVenueForm'
                     });
                   });
               </script>
           <?php
           break;
           case '5': ?>
               <script type="text/javascript">
                   jQuery(document).ready(function($) {
                     // var eventLabel = $('#event_label').val();
                     window.dataLayer = window.dataLayer || [];
                     window.dataLayer.push({
                       'event' : 'formSubmissionSuccess',
                       'formId' : 'contactForm'
                     });
                   });
               </script>
           <?php
           break;
         default:
           # code...
           break;
       } //end switch
     } //end function
     add_action("gform_post_submission", "gf_gtm_tracking", 10, 2);

Hey! Where exactly do I add this code into the backend of my site. I've added it into to the functions.php file underneath themes > divichild > functions.php, however I am still not seeing the inputed data from the form submission. Could really use your help!