I’m making this public even though it’s off-topic because lately I’ve seen a lot of people asking.

You can’t comment on or reply to a note on or reply to your post. The only way to do it is to copy-and-paste the note/reply into a new text post and put your response there. (Big tip: when your first paste it, it’ll likely be invisible due to the white font. Click the HTML button for your post, then just hit Cancel. That normally “resets” it into black font automatically.)