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. 
CometChat.deleteConversation(UID, CometChatConstants.RECEIVER_TYPE_USER, new CometChat.CallbackListener<String>() {
  @Override
  public void onSuccess(String s) {
    Log.d(TAG, s);
  }

  @Override
  public void onError(CometChatException e) {
    Log.d(TAG, e.getMessage());
  }
});
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