Confusion about where to enter office equipment deductions

Are you in Schedule C in your 1040?  TurboTax Business is for returns  for partnerships, S-Corporations, and trusts/estates.  Since you are a single member LLC you should be preparing Schedule C in your personal return.

To elect to take the De Minimis election (rather than depreciate the assets over time), please follow these steps:

Part 1.  Make the De Minimis election

1. Click on the Business tab > Continue > I'll choose what to work on
2. In the Business Income and Expenses section, click the Start/Update button.  
3. If you have already started adding information about your business, you will see the Here's the business info we have so far screen.  Click on Edit next to your business.
4. If you haven't already started adding information about the property, continue through the screens to enter the needed information.
5. You will now be on the Your [business name] Business screen.  
6. In the Business Assets section, click on the Start/Update box.
7. When you come to the screen, Did you buy any items that each cost $2,500 or less in 2015? mark the Yes button and click Continue.  
8. On the screen Let's see if you qualify to deduct these items as expenses, mark both of the Yes buttons and click Continue.  
9. On the screen Now, let's review each item you bought  -- If you mark that every item cost $2,500 or less, you will be asked if you want to claim the improvements as expenses.  Select the No button since you're claiming them under the de minimus election.  You will be brought to the Business Summary screen.  Proceed with Step 2, below. 
10. If you mark that some cost above $2,500, proceed through the screens and answer Yes on the screen Do you have any items that aren't covered by your elections?  Proceed through the screens to enter these assets. 

Step 2.  Enter your election-related items as other expenses.

1. On the Your [XX] Business Summary screen go to the Business Expenses section and click on the Start/Update box next to Other Common Business Expenses. 
2. On the next screen, Let's write off some business expenses, scroll down to Other Miscellaneous Expenses screen and click on the Start/Update box.  
3. On the screen Any Miscellaneous Expenses? enter the description description and amount paid for the assets.
4. Click Continue when finished.