From Income Tax Withholding - Utah Income Taxes - Utah.gov:
For payer ID: The Utah withholding account number is a 14-character number. The first eleven characters are numeric and the last three are “wth.” Do not enter hyphens. Example: 12345678901wth.
The program wants lower case for wth. Contact the employer or payer of the income to get the Utah ID number. If there is no state withholding, you can delete the entire state line.