This wil help you create a custom meta. it has not been tested

additional_meta.php

  <?php
  
  add_action('add_meta_boxes', 'ceo_tribe_image_meta_box' );
  
      public function ceo_tribe_image_meta_box() {

        add_meta_box(
                'page_info_box_permission', __('Page Permission', 'tribe'), 'page_info_box_format', 'page', 'side', 'low'
        );
        
    }
    
    function page_info_box_format( $post ) { ?>

        <?php $format = get_post_meta( $post->ID, 'single_image_align', TRUE ); ?>
        <div class="form-group">

            <label>Select Post Format</label>
            <select name="single_image_align" class="form-control">
                <option value="top" <?php selected( $format, 'top'); ?>>Top</option>
                <option value="center" <?php selected( $format, 'center'); ?>>Center</option>
                <option value="bottom" <?php selected( $format, 'bottom'); ?>>Bottom</option>
            </select>
        </div>

    <?php }
    
    function tribe_single_box_save($post_id) {
        if (isset($_REQUEST['single_image_align'])) {
            update_post_meta($post_id, 'single_image_align', $_POST['single_image_align']);
        }
    }
    add_action( 'save_post', 'tribe_single_box_save' );
    
    

Thanks homie