The 500-UET form is used when someone has a underpayment of taxes for the year bu they want to appeal that penalty on their tax return for the current year. The form will provide the necessary information to the department of revenue showing that you paid more taxes this year than you did the prior year but still didn't pay enough. You need to find last year's returns to determine how much you had withheld. If you used Turbo Tax last year, you should be able to open last year's file and look for those entries. If you didn't, hopefully, you have hard copies of last year's returns.