How do i enter in base cost of goods sold for schedule C in the TurboTax app?

TurboTax personalizes the list of expenses that it'll ask for depending on the type of business you have.  I would suggest that you go back to the questions regarding your business and make sure that you entered the correct type of business.  Generally, if it is a business that carries inventory, the program will ask you all the necessary questions to calculate your COGS.   To get back to your Schedule C:

1. Open or continue your return
2. Locate the Schedule C section
3. Go to Schedule C
4. Under the business you need to review, go to Review
5. Change your Work description if needed
6. Once make the change, continue the interview until you get to the expense categories (see the image below)
7. Select Inventory the program will guide you as you enter the information. If it doesn't come up, you can try at the end under "Less Common Expenses."