Where do I enter Schedule C, line 21 Repairs and Maintenance?

When you're on the business income and expense summary screen, click on Add expenses for this work under Expenses.

TurboTax will recommend some common expense categories based on the information you've entered about your business so far. If repairs and maintenance expense is not listed there, scroll down to the Less Common section. 

You can page through the various expenses (they should be in alphabetical order), or you can type Repairs in the search bar. When you see the expense category, select the check box next to it and then click Continue.

I figured it out. TurboTax lists some of the possible expenses and wants me to select others that I plan to use this year. It does not show the categories I used last year. This step is to select extra categories, but I thought that this was the place to actually add dollar amounts. Not clear, but I did find the correct list of categories later. I don't remember it being this hard in years past.