Hello,
This is a sample of how to center a table (you can test it with the file TemplateHTML.docx included in the package):
<?php
require_once 'classes/CreateDocx.inc';
$docx = new CreateDocxFromTemplate('examples/files/TemplateHTML.docx');
$docx->replaceVariableByHTML('CHUNK_1', 'block', '<table align="center"><tr><td>AAA</td><td>AAA</td></tr><tr><td>BBB</td><td>BBB</td></tr><tr><td>CCC</td><td>CCC</td></tr></table>', array('parseDivsAsPs' => true));
$docx->createDocx('output');
It's tested and working as expected.
Regards.