You don't get a "credit" (which has a specific meaning in the tax world), but you do get a deduction.
Did you make this contribution through your employer (through a payroll deduction plan)? If so, then the $3,400 was removed from Wages in boxes 1, 3, and 5 on your W-2. It's not reported as a deduction because it was never in your income in the first place - that's your tax break.
Note that this amount will appear on your W-2 in box 12 with a code of W.
On the other hand, if you made this contributions directly to the HSA (outside your employer), then you report this amount in the HSA interview (Federal->Deductions & Credits->Medical->HSA, MSA Contributions) by navigating to the screen "Let's enter your HSA contributions' (see screenshot below), and entering the 3,400 on the second line as "personal" contributions.
