Here’s a clearer and more concise version:
I’ve reserved a seat but haven’t activated my pass yet. I’ve decided to change my travel date, but I wasn’t able to cancel the reservation. Can I make a new reservation for a different date and simply not use the original one?
If you want it slightly more formal (for customer support), you could say:
I have reserved a seat but have not yet activated my pass. As I need to change my travel date and was unable to cancel the original reservation, could you please confirm whether I can book a new reservation and leave the previous one unused?
and would this affect in any way my past day travels?
