How do I edit a modified payroll check?

Use Modify Payroll Checks to edit payroll data. How you edit the paycheck depends on whether the payroll check was printed.

Yes, the paycheck is printed. Use the option to Void and Reset in Reports > Payroll Checks to edit the paycheck. First, select the check number from the list of printed checks on the Reprint tab. Second, click Void Check Number and Reset for Reprint. Third, use Employees > Enter Payroll Checks to edit the paycheck. Click Calculate Pay Codes (CTRL+C) to compute the paycheck. Finally, use Reports > Payroll Checks to reprint the paycheck.
No, the paycheck is not printed. Use Enter Payroll Checks to edit the paycheck. Click Edit (CTRL+E). Enter the reference number to look up the paycheck. After you edit the paycheck, click Calculate Pay Codes (CTRL+C) to compute the paycheck.