Once Single Touch Payroll (STP) has been reported to the ATO, there's no way to undo or delete the Event.
To correct values in myGov; a supplementary pay slip is required. Once a supplementary payslip has been reported to the ATO via STP2, the employees' YTD values will be updated.
Creating a Supplementary payslip to correct reported STP figures.
To correct values in the Business Portal, modify the values manually in the Business Portal.