Hello Reecekai45
From where do you know that you are not seated together? The seat numbers on a train are somestimes not in a logical, subsequent order.
Bear in mind: The system is allocating the seats next to each other if possible - provided there are enough seats left. The line is very busy in spring, summer, and automn. It is therefore well likely the train to be fully booked.
There is no e-mail contact, and contacting SBB through the contact form is inefficient. SBB can be contacted by chat, however, provided you ask the chat bot to connect you with an agent:
https://sbb-tickets.cc/en/help-and-contact/chatbot.html#anchor4
You can also try changing the seats yourself: go to trenitalia.com, modify the ticket using the PNR as given on the ticket. Beware that once you have accessed the ticket through the Trenitalia website, SBB cannot access/refund the ticket any longer on your behalf.
Kind regards,
Roland