How do I correct the vacation balance for an employee who should not have the standard 25 vacation days?

You can adjust vacation days for an employee by going to Vacation in the menu on the left and then Adjust Vacation Days. Here, click on Adjust Vacation Days (blue button) and for 'day,' enter a minus (-) before the number of days to subtract, then search for the employee at the bottom. You may want to add a comment, as this will appear in the employee's profile.