add_action( 'admin_head', 'remove_my_meta_boxen' );
function remove_my_meta_boxen() {
    remove_meta_box( 'postimagediv', 'countries', 'side' );
    add_meta_box('postimagediv', __('Country Flag'), 'post_thumbnail_meta_box', 'countries', 'side', 'high');
}

The post type in this example is countries

<a href="javascript:history.go(-1)" class="custom_back_button"><i class="fas fa-chevron-left"></i> Back</a>

This example uses Font Awesome. Don’t forget to include Font Awesome lib in your functions.php

jQuery(document).ready(function($) {

  // Test
    console.log( "ready!" );
  

});

Meta Box – WordPress Custom Fields Framework

The code below relates to the meta box plugin. And the code below relates to 2 custom post types. Players and Coaches. And then adding meta fields to those custom post types.

// Custom Post 1
      register_post_type( 'coaches',
          array(
              'labels' => array(
                  'name' => __( 'Coaches' ),
                  'singular_name' => __( 'Coach' )
              ),
          'public' => true,
          'has_archive' => true,
          'supports' => array('title', 'editor', 'thumbnail')
          )
      );
    register_taxonomy_for_object_type( 'category', 'coaches' );
// Custom Post 2
      register_post_type( 'players',
          array(
              'labels' => array(
                  'name' => __( 'Players' ),
                  'singular_name' => __( 'Player' )
              ),
            'public' => true,
            'has_archive' => true,
            'supports' => array('title', 'editor', 'thumbnail')
          )
      );
    register_taxonomy_for_object_type( 'category', 'players' );

// Meta Fields
  function add_meta_fields( $meta_boxes ) {
    $meta_boxes[] = array(
      'id' => 'twitter_url',
      'title' => 'Twitter Url' ,
      'post_types' => array( 'players','coaches' ),
      'context' => 'normal',
      'autosave' => false,
      'fields' => array(
        array(
          'id' => 'twitter_url',
          'type' => 'url',
          'name' => 'URL',
        ),
      ),
    );
    $meta_boxes[] = array(
      'id' => 'instagram_url',
      'title' => 'Instagram Url' ,
      'post_types' => array( 'players','coaches' ),
      'context' => 'normal',
      'autosave' => false,
      'fields' => array(
        array(
          'id' => 'instagram_url',
          'type' => 'url',
          'name' => 'URL',
        ),
      ),
    );
    $meta_boxes[] = array(
      'id' => 'facebook_url',
      'title' => 'Facebook Url' ,
      'post_types' => array( 'players','coaches' ),
      'context' => 'normal',
      'autosave' => false,
      'fields' => array(
        array(
          'id' => 'facebook_url',
          'type' => 'url',
          'name' => 'URL',
        ),
      ),
    );

    return $meta_boxes;
  }
  add_filter( 'rwmb_meta_boxes', 'add_meta_fields' );

Below is how to add a location/Address field

// Address
    $meta_boxes[] = array(
      'id' => 'address',
      'title' => 'Address' ,
      'post_types' => array( 'countries' ),
      'context' => 'normal',
      'autosave' => false,
      'fields' => array(
        array(
            'id'   => 'address',
            'name' => 'Address',
            'type' => 'text',
        ),
        array(
            'id'            => 'map',
            'name'          => 'Location',
            'type'          => 'map',

            // Default location: 'latitude,longitude[,zoom]' (zoom is optional)
            'std'           => '-6.233406,-35.049906,15',

            // Address field ID
            'address_field' => 'address',

            // Google API key
            'api_key'       => 'AIzaSyBVKag0eBXXIjS0rvi6qUYZ9sScw5kNeXQ',
        ),
      ),
    );

ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);