Hello,
It is not possibile to change the ticket directly. I suggest you buy a new one and ask for a refund via our online form.
If you have an international ticket, you will need to call our Contact Center at 0848 44 66 88
(CHF 0.08/min.) or +41 51 225 78 56, if you are abroad.
I wish you a lovely day,
Chiara_S