You haven't got much time to do this (April 15th for an amended return from 2015), so let me tell you a way that is most likely to succeed the first time.
First, I assume that you have copies of all the HSA information from 2015, like your W-2s, 1099-SA(s), and forms 8889.
I suggest that you delete all the HSA information from your 2015 return and start over. This will erase all HSA entries both good and bad, but it will save you having to mess around trying to change entries.
To delete the 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.
