Auto-populate Custom Post Type Title with ACF field.

functions.php

<?php
// Auto-populate Staff post title with ACF name field.
  function efd_staff_post_title_updater($post_id)
  {
      $my_post = array();
      $my_post['ID'] = $post_id;

      if (get_post_type() == 'staff') {
          $my_post['post_title'] = get_field('name');  // Update Title
          $my_post['post_name'] = get_field('name'); // Update Slug
      }

    // Update the post into the database
    wp_update_post($my_post);
  }

  // run after ACF saves the $_POST['fields'] data
  add_action('acf/save_post', 'efd_staff_post_title_updater', 20);