Give the Right Audience Access to Chatter Posts
Users can change which users or groups can view a post. Changing an audience on a post can share it with more people for added input, or restrict visibility to make sure that confidential information only reaches the right users.
Where: This change applies to Salesforce for Android and Salesforce for iOS version 18.0, in all editions except Database.com.
How: Each user can edit their post visibility inside the publisher.