I want to add an
<?php submit_button( __( 'Update Media' ), 'primary', 'save' ); ?>
submit_button($text, $type, $name, $wrap, $other_attributes) is located in the /wp-admin/includes/template.php file on line 2169
submit_button(..) It then does a call on
get_submit_button($text, $type, $name, $wrap, $other_attributes) which is located in the same file on line 2190.
Unfortunately there is no apply_filters to modify the output of the WordPress. In that case you have to make changes in the WordPress core files. I do not suggest you make any change in the WordPress core files, because on next update you will lose that changes.