This can happen in the desktop version of the software (which you have). To find the "Unmark Estimated" from the Edit menu", go to the top left to Edit (between File and View), and click on it.
Halfway down is "Unmark Estimated". Click this and the field will be unmarked. (as you can see, to mark a field, do the same thing but click on "Mark as Estimated").
The real problem is trying to find which field TurboTax is talking about. It should be marked with a red letter (an exclamation point, perhaps, but it isn't always visible). If you click on fields on the 8889-S one by one and none appear to be marked as estimated, then the fastest thing to do may be to just delete your HSA data and start over.
To delete your HSA data, please do the following:
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. go back and redo the entire HSA interview.
