If you have a casualty and/or theft loss on property used 100% for business, you will report the loss on IRS Form 4684 Casualties and Thefts, in Section B for business property. You will need to enter this through the Business Income topic of the Federal Q&A.
To enter or review business casualty/theft losses:
Once this information has been entered, your loss will carry to Line 14 of IRS Form 4797 Sale of Business Property. Your total gain/loss will then be carried to Line 14 of Form 1040.