Delete your message
Whether you send a message to the wrong conversation, chat or if you accidentally made an announcement, you can delete it right away simply by hovering the mouse over the message so the three-dotted menu appears (on the right side of the message), and by selecting "delete" from the menu.
A confirmation dialogue will pop-up, all you need to do here is to click the delete button. Or if you've changed your mind, you can just close it.
info_outline Note that the delete action cannot be undone, you will have to send a new message instead.