I found it 😀 Yeeeeeeeeaaaahhhhhh :))))
This is final code that worked! I explained each level 😉
/* for get author ID use these */
$curauth = (isset($_GET['author_name'])) ? get_user_by('slug', $author_name) : get_userdata(intval($author));
$author_id = get_the_author_meta('ID');
/* First condition */
if( get_the_author_meta('management_certi', $author_id, true)) {
/* get file ID */
$id = get_user_meta( $author_id, 'management_certi');
if($id) {
/* Array Loop! */
foreach($id as $attachments) {
/* get file URL */
$url = wp_get_attachment_url( $attachments ); ?>
<a href="https://wordpress.stackexchange.com/questions/224739/<?php echo $url; ?>" data-lightbox="image-1" data-title=""><img src="https://wordpress.stackexchange.com/questions/224739/<?php echo $url; ?>" class="thumbnail" width="36" height="36" /></a>
<?php
}
}
} else { echo '--'; }