This screen is not exactly editable, since it is part of the core of Wordpress. But you can customize a few things by adding a css to your admin.
For example, I was able to center the button first by adding a css with this line in the functions.php of my theme:
$my_theme_versao = '1.0.0.0';
function my_theme_admin_enqueue($hook) {
global $my_theme_versao;
wp_enqueue_style('my_theme-admin-style', get_stylesheet_directory_uri() . '/admin.css', array(), $my_theme_versao);
}
add_action('admin_enqueue_scripts', 'my_theme_admin_enqueue');
And in css, with the rules being more specific than the original Wordpress css, as an example below:
body .media-toolbar-primary.search-form {
float: none;
text-align: center;
}
body .media-modal-content .media-toolbar-primary .media-button{
float: none;
}