The employer contributions should normally be added to your contributions by payroll deduction and put into box 12 on your W-2 with a code of "W".
If the employer did not include its contribution to your HSA in box 12 with code W, then, yes, you can add that amount to the dialogue that you referenced: "Did your employer tell you about any other contributions? Employer and payroll contributions not reported in Box 12 of your W-2."
However, you should contact your HR department to ensure that in addition to Box 1, that all HSA contributions from your employer and from you through a payroll deduction scheme should have also been removed from Wages in boxes 3 and 5. Otherwise, you will overpay social security and Medicare taxes.
