Here are the instructions about how to void a paycheck with Assisted Payroll.  However, I recommend giving them a call so they can walk you through it to make sure everything's entered properly especially if the paycheck was issued in a prior quarter.  You can never be too careful when it comes to payroll taxes.

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You can void a paycheck after you send it to the Assisted payroll service. If the void is received after processing begins, tax funds may be applied to future payrolls in the same quarter. If the paycheck is in the last payroll of a quarter, tax funds may be refunded by the taxing agencies and an amendment may be required to correct tax filings.

If an amendment is necessary, contact QuickBooks Assisted Payroll support to start the amendment process. (You may be charged a fee for this service.)

Note: We recommend that you back up your data before you void paychecks.

To do this task:

1. Go to Employees > Edit/Void Paychecks.
2. Enter a date range in the Show paychecks from and through fields, and press the Tab key to display the checks.
3. Select the paycheck(s) you want to void.
4. Click the Void button.  
5. Check to make sure that VOID: is shown in the Memo column and the net amount of the check is now 0.00.
6. Once you have read the message that appears, check the checkbox and click Continue. These messages vary based on the check date and the time you start the void process.
7. In the Confirmation and Next Steps window, click Send Information to Intuit to ensure that your voided paycheck information is sent to the payroll service. You will need to provide your Payroll Service PIN.
8. Click Done to close the Edit/Void Paychecks window.