Even when you are part of a group conversation, you can privately respond to another individual.
Tap the Inbox icon [ 1 ].
Select the Conversation
Once you tap the Conversation, the To list [1] will display the recipient's name. The conversation is a private conversation you can't add recipients to it.
Type a message in the message field [2]. When you have finished, click the Send button [3].
The message will sent to the person in the To field and not to everyone else.
You can view the sending status saying that your message was sent successfully or not.
View the sent message. The newer messages appear at the the top.