Hello Kabueyi83
If you purchased the ticket from SBB, please call SBB: +41 51 225 78 56 (24/7, waiting times may occur). Ticket,changes are only possible through phone or at the ticket office.
Alternatively, you can try to amend your ticket through Trenitalia: https://trenitalia.com. Kindly note: If you purchased it from SBB and you are going to amend it through Trenitalia, SBB cannot help you / access the ticket any further.
Kind regards,
Roland