The reopening process is nightmare, really. It wasn’t usable discussion setting. Bad experience for WordPress users. Previously, for some weeks, I did a live test to check the usability of closed comment in WordPress blog.
To re-enable all comments open, users should refer to the discussion setting panel. Check
Allow people to post comments on new articles and uncheck
Automatically close comments on articles older than [numeric] days. But, it wasn’t that easy! For the all new posts after closing comments stated, users must have to re-allow post comment manually. Go to the "Posts" panel, hovering mouse to the post title, choose "Quick edit" menu, check "Allow comments", then remember to click the "Update" button. Do it per post manually!
I think, I need this feature:
Automatically re-open comments on articles older than [numeric] day.