You can delete your chat via the zapptales app at any time you want.
Android: Open the zapptales app, go to “My chats”, click on the chat for a few seconds and choose “Delete”;
iPhone: Open the zapptales app, go to “My chats” and swipe from right to left in order to delete it;
Important: this process of deleting cannot be undone. Your data and what you edited until then will be deleted. If you want to edit your chat again afterwards you will have to export the chat from WhatsApp, Facebook Messenger, Instagram, iMessage, Threema or Telegram and start editing it again.