You'll have to prepare Form W-2c, Corrected Wage and Tax Statement, for each employee who received an incorrect W-2 form. Let's also prepare W-3c, Transmittal of Corrected Wage and Tax Statements, to accompany the W-2c forms. Then, file both W-2c and W-3c forms to the government.
For more details on how to amend filed W-2 forms, refer to this article: Correct or amend W-2 forms. This link provides a detailed explanation or instructions from correcting, printing, and filing the form.
I've also added a link for more tips and managing your payroll in QuickBooks Online (QBO): Payroll 101. It contains essential info you need with payroll tasks, from paying employees to taking care of taxes.
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