On the box 12 has only the amount which my employer matched. How do I enter the amount which I paid?

The amount in box 12 with a code of "W" on your W-2 should be the sum of the employer contributions to your HSA and your contributions through a payroll deduction plan.

It's counter-intuitive, but the IRS refers to both of these as the "employer contribution".

The first thing you have to do is ask your employer if they removed both your and the employer's HSA contributions from Wages in boxes 1, 3, and 5 on the W-2. HSA contributions are not subject to federal income tax, Social Security tax, or Medicare tax.

If your employer did not remove even their own HSA contributions from Wages, then you need to ask for a corrected W-2 and ask them why they don't complete the W-2 according to the W-2 Instructions from the IRS.

If your employer did remove both your contributions from Wages (making them pre-tax), then the way you enter this (because the employer's own contributions were already entered in box 12) is to go to the screen entitled "Did your employer tell you about any other contributions?" (see screenshot below) and click on "yes" to expose the bottom three lines.

You enter the amount that was your payroll deduction (not the employer's part) in the bottom line (see red arrow).

If your employer failed to remove your part of the HSA contribution (i.e., your contribution was after-tax), then go to the screen entitled "Let's enter [your name] HSA contributions" (see screenshot below), and enter your part of the payroll deduction in the second line.

Note that the HSA contributions shouldn't be handled this way, and if your employer failed to remove either his own  contributions or yours from Wages in boxes 3 and 5, then you are overpaying on Social Security taxes and Medicare taxes, but we have no way to fix that on the income tax return.

You need to have a discussion with your HR department in any case.