Casualty and Theft losses are reported on IRS Form 4684 for both personal and business. See IRS tax topic -https://www.irs.gov/taxtopics/tc515.html
However, claiming a theft loss without filing any type of police report or insurance claim for proof of loss would more than likely be denied by the IRS if ever questioned about the loss.
To enter business income and expenses (Schedule C) you will need to upgrade to Home and Business using the online editions.
To report a Casualty or Theft -
- Click on Federal Taxes (Personal Using Home and Business)
- Click on Deductions and Credits
- Click on I'll choose what I work on (if shown)
- Scroll down to Other Deductions and Credits
- On Casualties and Thefts, click the start or update button
