You can view this video for step by step directions:
https://www.loom.com/share/c59dbe9e94734467b862196739659198
Here are the written steps 😀
1. Choose 'Inbox' from the Messaging menu on the left
2. Choose the message you wish to send a reply to
3. Type your message in the message bar at the bottom of the card
4. Click the send message icon, that resembles a paper airplane, to reply to an existing email or SMS conversation