Click on the care team for which you have a notification.
Here you can see a red badge with the mention 1 new discussion thread and the team is highlighted.
Then click on the message that shows the red badge with the mention Unread Discussion Thread.
The new discussion thread is now open!
You can reply to the message using the text box at the bottom of the page.
Then send your message by clicking on the upward-pointing arrow in the purple circle at the bottom right.