You can't override it, but you may want to go back through the Home Office section to make sure all information is answered correctly (see below). The most common reason for a home office to be disallowed is due to not having a "net profit" from your business.
Your "net" profit is the amount after expenses. This would include vehicle expenses, advertising, supplies, etc. If you still had a net profit after that, you should get the Home Office deduction. You can check your net profit by previewing your 1040. Line 12 of your 1040 will show the business profit or loss.
How do I Preview my TurboTax online return before filing?
How to get to the area to review your home office expenses : While inside the software and working on your return, type Schedule C in the Search at the top of the screen (you may see a magnifying glass there). There will be a popup that says Jump to Schedule C. Select that to get to the general area.
- select Edit next to your business (if it is there)
- scroll to Business Expenses
- then Home Office