Hi Mohseen
Thank you for your question.
To answer this question, we will have to check the kind and validity of the voucher.
Please call the SBB Contact Center at 0848 44 66 88 (0.08/min) and give my colleagues the voucher code, they will be able to give you an answer. Alternatively, you can bring the voucher at any SBB ticket counter and ask.
I wish you a nice day
EleonoraS