To access that area of your return, type "home office" in the search box and click on the "Jump to" link that appears in the search results. That will take you to "Your 2018 self-employed work summary" screen. Then, click "Review" next to your business name. On the next screen, if you don't see your Home office information, click on Add expenses for this work. You'll "Home office" at the top of the list. (see sample screenshot below)