Sometimes we wish to message a specific person within a thread, and have certain people left out from that content. And sometimes we wish to include new members to a thread, and have them exposed to all the previous discussion. To do this- scroll over a specific message, and tap the reply icon. You can choose to add recipients by tapping on the ‘to’ which is located to the right of the threads current members. In order to remove a specific person, tap on their name then press remove.