You want to modify this line in qa-page.php:
$qa_content['logo']='<A HREF="'.qa_path_html('').'" CLASS="qa-logo-link">'.qa_html(qa_opt('site_title')).'</A>';
Replace qa_path_html('') with whatever you want for your link.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.