How can I enter a K-1 from form 1120S. Box 11 on my K-1 is labeled "Section 179 deduction" but there's no option for that in the TurboTax form (I'm using premier).

You may have been entering a K-1 on the form for an partnership rather than an S-Corp.  You will have to create the K-1 in the S-Corp section and then delete the K-1 from the Partnership section.

When entering the information, please make sure you use the correct K-1 entry form. There are actually three types of K-1s, depending on the type of entity creating the K-1: partnership, S-corporation and trust/estate.  Lines and codes on the forms differ from each other.

To enter information from Schedule K-1 (1120S), please follow these steps:

1. Click on Federal Taxes > Wages & Income
   
2. Under S-corps, Partnerships, and Trusts, click on the Start/Update box next to Schedule K-1.
3. On the Tell Us About Your Schedules K-1 screen.  Click on the Start/Update box next to S Corporations (Form 1120S).   [The second one in the list.] 
4. If you haven't started entering K-1 information, on the next screen, enter the S Corp. name and address and click Continue. 
5. Continue through the screens, entering the information.  Be sure you have marked the box for line 11. 
6. You should see eventually see the screen, Enter Box 11 Info.  Fill in the box for Section 179 Deduction from your K-1.
7. You will eventually be brought back to the screen, Tell Us About Your Schedules K-1.  
8. Click the Update box next to Partnerships/ LLCs (Form 1065).
9. You should see the Partnership/LLC K-1 Summary.  Click the Delete icon (trashcan) next to the entry.
10. Click the Done box.
    

[Edited | 4/15/2020 | 8:51am PDT]