Hello there, Aline3.
I order for us to guide you on how to update back dated paychecks, we'd need some more information. I'd recommend reaching out to our phone support agents. Our payroll correction team will guide you thoroughly on how to achieve this one as they do a screen sahre and look at the previous payments and guide you on changes to the employee settings.
Feel free to browse this article for the complete list of articles about this payroll service: QuickBooks Online Advanced Payroll Hub.
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I'm just a post-away if there's anything that I can help with. Keep safe!