While deleting a Message is straightforward, receiving events for deleted messages with CometChat has two parts:
  1. Adding a listener to receive real-time message deletes when your app is running.
  2. Calling a method to retrieve missed message deletes when your app was not running.

​
Delete a Message

In other words, as a sender, how do I delete a message? In case you have to delete a message, you can use the deleteMessage() method. This method takes the message ID of the message to be deleted. 
CometChat.delete(messageId: 12345, onSuccess: { (baseMessage) in

   print("message deleted successfully. \(baseMessage)")

}) { (error) in

   print("delete message failed with error: \(error.errorDescription)")
}
Once the message is deleted, In the onSuccess() callback, you get an object of the BaseMessage class, with the deletedAt fieldset with the timestamp of the time the message was deleted. Also, the deletedBy field is set. These two fields can be used to identify if the message is deleted while iterating through a list of messages. By default, CometChat allows certain roles to delete a message.
User RoleConversation TypeDeletion Capabilities
Message SenderOne-on-one ConversationMessages they’ve sent
Message SenderGroup ConversationMessages they’ve sent
Group AdminGroup ConversationAll messages in the group
Group ModeratorGroup ConversationAll messages in the group

​
Real-time Message Delete Events

In other words, as a recipient, how do I know when someone deletes a message when my app is running? In order to receive real-time events for the message being edited, you must add protocol conformance CometChatMessageDelegate as Shown Below : 
extension ViewController: CometChatMessageDelegate {

		func onMessageDeleted(message: BaseMessage) {

        print("received deleted message successfully.")
    }
}

​
Missed Message Delete Events

In other words, as a recipient, how do I know if someone deleted a message when my app was not running? When you retrieve the list of previous messages, for the messages that were deleted, the deletedAt and the deletedBy fields will be set. Also, for example, the total number of messages for a conversation are 100, and the message with message ID 50 was deleted. Now the message with id 50 will have the deletedAt and the deletedBy fields set whenever it is pulled from the history. Also, the 101st message will be and Action message informing you that the message with id 50 has been deleted. For the message deleted event, in the Action object received, the following fields can help you get the relevant information-
  1. action - deleted
  2. actionOn - Updated message object which was deleted.
  3. actionBy - User object containing the details of the user who has deleted the message.
  4. actionFor - User/group object having the details of the receiver to which the message was sent.
In order to edit or delete a message, you need to be either the sender of the message or the admin/moderator of the group in which the message was sent.