I'm here to help share information about the difference between voiding and deleting transactions in QuickBooks Desktop (QBDT).
Voiding changes the amount of the transaction/s to zero but it keeps a record of the transaction/s in QuickBooks. However, deleting the transaction/s in QBDT will remove the transaction/s entirely in QuickBooks.
In your case, it's your preference to either void/delete the duplicate check to your vendor. If you want to remove the check entirely in QBDT, then, you may delete it. If not, you can just void the check to zero out the amount.