On your W-2, do you have an amount in box 12 with a code of R or W?
Multiple possibilities come to mind.
First, did you auto-import your W-2? HSA contributions through your employer are indicated by a code of W in box 12 on your W-2. If, however, your auto-import failed, then some garbage may have been interpreted as a code W with an amount that has confused TurboTax.
The way to fix this is to get a copy (or write the information down), delete your imported W-2 in TurboTax, then re-enter it manually (i.e. when you are asked for the employer's EIN, just continue to the next screen and enter all the data manually from the W-2).
Second, it may happen that TurboTax has become convinced that you made this contribution, whether by a faulty W-2 or because of an entry that you later changed, and nothing you do will change its mind. That is, once entered, the amount persists in TurboTax no matter what you do.
The way to fix this is to delete all the HSA data from your return. If you really don't have an HSA and never intended to file form 8889. I suggest you do the following:
***HSA Reset***
1. make a copy of your W-2(s) (if you don't have the paper copies)
2. delete your W-2(s) (use the garbage can icon next to the W-2(s) on the Income screen
*** Desktop***
3. go to View (at the top), choose Forms, and select the desired form. Note the Delete Form button at the bottom of the screen.
*** Online ***
3. go to Tax Tools (on the left), and navigate to Tools->Delete a form
4. delete form(s) 1099-SA (if one), 8889-T, and 8889-S (if one)
5. go back and re-add your W-2(s), preferably adding them manually
6. continue with your return. in 99% of the cases, this will delete any HSA data (like that $6,000).
The other cases are rather rare:
1. You told TurboTax that your spouse made HSA contributions to your HSA (in the W-2 section).
2. You entered a 1099-R (money from a retirement account) and indicated that it went to an HSA.
3. You entered a 1099-SA to indicate a distribution that was the result of the death of an HSA holder who was not your spouse.
4. You entered the HSA interview (for whatever reason) and indicated that you overfunded your HSA in the previous year. This appears as a contribution in the current year.
NOTE: if you do not have an HSA and see the question, "What kind of High Deductible Health Plan coverage did you have on December 1, 2017?", be sure to answer "None" because this question does not apply to you.