Hello,
Thank you for contacting us.
At the moment Italiarail is not offering railpass services, only point-to-point tickets. You can book seat reservations on https://www.interrail.eu/en, https://www.raileurope.com/en/destinations/passes/eurail-global-pass, or https://www.eurail.com/en.
If you are having trouble booking I would recommend reaching out to Eurail directly.