If the paycheck is entered using the QuickBooks Online Payroll service, you'll need to delete and recreate it. This way, you would be able to edit the net pay.
If the paycheck is entered as a Check, edit the check by changing the amount. Go to the Vendor/Contractor profile, select the check and edit the amount.
If the paycheck is entered using a Journal Entry, go to the Vendor/Contractor profile, select the journal entry and edit the amount.
Please click on this link to see more help articles about managing payroll in QuickBooks Online.
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