Unfollow a Record

Call a method to stop following a record.
When you follow a record such as a user, the call to ConnectApi.ChatterUsers.follow returns a ConnectApi.Subscription object. To unfollow a record, pass the id property of that object to deleteSubscription(communityId, subscriptionId).
ConnectApi.Chatter.deleteSubscription(null, '0E8RR0000004CnK0AU');