Train cancelled on first day of travel: need to change start day after I have already activated it.

My train was cancelled after my journey started. I therefore need to change the start day on my Global pass AFTER the start of the first day for which it is activated, since the cancellation of trains (with no other possibility to travel on the same day) was through no fault of my own. Please help. I did not leave the start country (switzerland) before the cancellation occurred and I had to go back. I have a General-Abo, meaning all my trains are already paid for within switzerland, so I have not used the Global pass at all yet for any journey. It is however already activated for today.