When you use an auto for business, any amounts you depreciated are subtracted from the basis of the property to determine gain or loss. You will have to see how much depreciation or depreciation equivalent was deducted in prior years,
For passenger automobiles, you allocate the property's use on the basis of mileage. The percentage of qualified business use is by dividing the number of miles you drove the vehicle for business purposes during the year by the total number of miles you drove the vehicle for all purposes (including business miles) during the year. You stop depreciating property when you have fully recovered your cost or other basis.
If you used the standard mileage rate for the business use of your car, depreciation was included in that rate. The rate of depreciation that was allowed in the standard mileage rate is shown in the Rate of Depreciation Allowed in Standard Mileage Rate table. You must reduce your basis in your car (but not below zero) by the amount of this depreciation.
In the vehicle section, say you converted it to personal use. Then MANUALLY calculate things and report it in the "Sale of Business Property" section. If you don't know how to manually calculate things, you may want to go to a tax professional.