Yes—rescheduling to September 21 should be allowed without losing the voucher, as long as all of these are true:
- The new exam date is still on or before the voucher’s exam completion deadline of October 20.
- The reschedule is done at least 24 hours before the current appointment.
- The voucher’s own promotional terms do not add a stricter restriction.
Based on the policy in the provided material, the key requirement is that the exam must be scheduled and taken before the voucher expiration date. In this case, moving the appointment from September 18 to September 21 stays within the completion window you listed, so the passed booking deadline of August 15 should not by itself cause voucher loss.
For fees, Microsoft’s reschedule and cancellation policy says to reschedule or cancel at least 24 hours before the scheduled exam or the fee or voucher may be forfeited. Since September 13 is more than 24 hours before September 18, that timing meets the standard policy window.
To reschedule:
- Sign in to the Learn profile.
- Open Profile from the avatar menu.
- Go to Credentials > Certifications.
- Find the exam appointment and select Reschedule.
- Complete the change on the exam delivery provider’s site.
If the system blocks the new date, that usually means the voucher has a program-specific restriction, and the next step is Microsoft Credentials support or Pearson VUE support.