You can manually change the userid values in the qa_posts table, then click the various recalculate buttons at the bottom of the 'Stats' section of the admin panel, to make sure all counts are consistent.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask 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.