It is just a tip, as this feature is not yet built in (v1.6.2).
You have a comment that is actually the answer and you want to convert comment -> answer.
1. you open phpmysqladmin
2. you open qa_posts and you search for the postid of the comment (see the anchor! #12345 of the commented link)
3. change type from "C" to "A"
4. /admin/stats and click "Recount Posts" to clean up.
Hope that helps.