If you want to unarchive a thread on Messenger, you have a couple of ways to do that. One is by manually unarchiving it. Here’s how to that:Open Messenger and go Archived Chats.Press and hold the thread that you want to unarchive.Select Unarchive.The other method to unarchive a message is to reply to a previously archived message, or to wait until a person messages you in that previously archived thread.