When you Edit your vehicle in Business Expenses, indicate that you 'stopped using it in 2018'.
Enter a Sales Price of the amount of your insurance reimbursement, and TurboTax will calculate any Gain/Loss for you. Leave 'Basis for Gain/Loss' and 'AMT Basis for Gain/Loss' blank.
If you claimed Actual Expenses for your vehicle, the Gain/Loss will be calculated on remaining Cost Basis, minus Prior Depreciation claimed.
If you claimed Standard Mileage, you will need to calculate and enter a 'Depreciation Equivalent' so TurboTax can calculate any gain/loss for you (screenshots).
When you set up your new Vehicle, enter the Cost as whatever you paid for it (insurance reimbursement, plus any additional amount) and date you started using it for business.