Add first and last name to post tags

<?php
// http://www.gravityhelp.com/forums/topic/post-tags-auto-populatecontent-template
// change the 15 to your form ID
add_action('gform_after_submission_15', 'add_name_as_tags', 10, 2);
function add_name_as_tags($entry, $form) {
        // read the post ID from the entry and the first and last name from the $_POST
        // change 6_3 and 6_6 to your form field IDs, using underscores
        $post = array( 'ID' => $entry['post_id'], 'tags_input' => array(rgpost('input_6_3'), rgpost('input_6_6')));
        // update the post
        wp_update_post($post);
}