If you have made an error in a message that has been sent or you have sent it in the wrong conversation you are able to delete and edit by:
1. Use your mouse to hover over the message
2. Click on the 3 dots to the left of the message
3. Select an option from the list
4. If you chose to 'Edit' the message you will notice the text appear back in the text box at the bottom of the communicate window. Once you are happy with your changes, click Save and it will update the original message text.
Messages are fairly instantaneous so although the message will update in the chat once amended, be aware that the other party may have already opened and seen the original prior to the change.