Hello Suleiny Rodriguez
Firstly, hello and welcome to the SBB Community.
Tickets cannot be altered. If you hold a ticket that allows its cancellation, you can do so and repurchase a new ticket at daily rate.
For cancellations you must call SBB: 0848 44 66 88 (CHF 0.08/min), from abroad: +41 51 225 78 56. Waiting times are possible. Alternatively, you can seek assistance at a railway ticket office.
Kind regards,
Roland