You can't reschedule the tickets booked using voucher and if you cancel ticket after 24 hrs you will lose voucher as well.
You can call customer care team and request to use it for 7th October.
Used Diners black and Marriott Bonvoy Diners card in first week of May to access this lounge.
If you have Diners black then you can swipe it 2 times to get access for 2 people.