I think you need an admin to re-open the topic so that you can amend it. AFAICT, this happened recently here:
Note though that this is not a QA-site but a forum. It's okay that topics are outdated. Answers are generally more ephemeral in forums and not amended years (you want to post on a topic created 8 (!) years ago—I believe nobody expects the answer to be what is currently state-of-the-art) after their creation.