In case you want to delete a conversation, you can use the deleteConversation() method. This method takes two parameters. The unique id (UID/GUID) of the conversation to be deleted & the type (user/group) of conversation to be deleted. 
String conversationWith = "UID";
String conversationType = CometChatConversationType.user;
await CometChat.deleteConversation(conversationWith, conversationType,
   onSuccess: (String str){
     debugPrint("Conversation deleted successfully at : $str");
   },
   onError: (CometChatException e){
     debugPrint("Conversation deletion failed : ${e.message}");
  	}
);
This method deletes the conversation only for the logged-in user. To delete a conversation for all the users of the conversation, please refer to our REST API documentation here. The deleteConversation() method takes the following parameters:
ParameterDescriptionRequired
conversationWithUID of the user or GUID of the group whose conversation you want to delete.YES
conversationTypeThe type of conversation you want to delete . It can be either user or group.YES