There is no way to directly change the check void date, but fixing the dates is still possible.  You need to unvoid the check and re-void it.

To unvoid the check:
  1. Find the check in the Payments tab in Accounts Payable and double-click it.
  2. Select Unvoid payment.  
  3. Choose an appropriate GL apply date- if the original void date was wrong, use this "wrong" date.
  4. Click OK. This will create the necessary journal entries and move the payment back into Open items as a negative.  Ignore the potential warning.
  5. As a convenience, you'll have the option of running the GL edit report to post these entries right away.  
Next you need to void the check again:
  1. Find the check in the Payments tab in Accounts Payable and double-click it.  
  2. Choose Void Payment.
  3. Choose the appropriate void date.
  4. Select or type in a void reason if desired.
  5. Do NOT create a debit memo since this decision would have been handled before.
  6. Click OK.   This will create the necessary journal entries and will also bring the Open item back up to the previous value.  
  7. As a convenience, you'll have the option of running the GL edit report to post these entries.  
When you examine Open items, it is possible that there is a $0 voucher for this payee.  If so, go to File Maintenance > Clear Fully Paid from Open Items and run this.  It should remove the $0 liability.