How to move UPLOADS folder in sub-domain which hosted in another server

Warning! Nothing of the proposed below was tested.

add_filter('upload_dir', 'update_attachment_url');
function update_attachment_url($data)
{
    $data['url'] = str_replace('http://main-domain/', 'http://sub-domain.com', $data['url']);
    $data['baseurl'] = str_replace('http://main-domain/', 'http://sub-domain.com', $data['baseurl']);

    return $data;
}

Code source.

Also you can try to change the values of upload_path and upload_url_path found in the wp_options MySQL table.

Remember to run Search Replace DB to change all published image paths.