Once a form has been approved and transferred to Payroll, the values cannot be edited anymore. The best way to do this is to have the user resubmit the form with the correct values. Before asking the staff to do so, please delete the form submitted so as to avoid any confusion.
Go to Classic:
Step 3: Delete the form that needs to be re-submitted by clicking on the "x" icon
Step 4: Ask the user to create a new form with the correct details and submit for approval.
Step 5: Do the Transfer to Payroll Process and generate a payrun so that the correct amounts are to be paid to the employee.