This is not autimatically build in yet, but you can create a .ics file (an event that people can add to their calendar) with this generator: https://www.terminsysteme.de/ics/, upload it to your google drive (make sure that it´s available to download for everybody) and add this link to the Forró app. That way, when people click on the link, they can download the event.ics file and add the event automatically to their calendar.