You can add an autoresponder to your form in seconds. Furthermore, you can create more than one autoresponder and switch between them. The custom autoresponder feature is available for paid plans only.
Go to Settings → Notifications → Form User Options and tick the option Send a confirmation message to the sender (autoresponder).
Enter the needed information and press Customize to create or edit autoresponders. However, the default autoresponder cannot be edited but you can create a copy of it.