PA02 date error

I made a mistake in PA02 when changing supervisor information on a position and can't figure out how to fix it. I set Update Employees to Y. I thought I had used today’s date as the effective date but as soon as I hit Add I saw that I had a typo and had entered the date as 01/14/5201. The message in the lower left corner said “update incomplete”. I tried to delete the position with the incorrect effective date but get a message “cannot delete; employee is in position”. There are 9 employees in this position and 5 of them updated, 4 did not. Is there a way to correct the effective date on this position, or delete it entirely and start over? Thank you