You don't call them to reschedule. You have to send them an email stating your list number, exam number, name and reasoning as to why you chose to reschedule. I forgot the exact email but it was something along the lines of:
CID@fdny or something.
Call 1(718)-999-2169 to get the email. That's the candidate investigation bureau.
My advice would be to not reschedule and just take it. If you choose to reschedule. You're looking at waiting months, possibly a year to retake it. Not a good idea.
Not rescheduling. I failed it and need to schedule my second attempt.