Since you're using the per-mile deduction and it's less than 100% business use, combined with the fact you took it out of service on your 2019 tax return, it "should" have been imported to your 2020 return. Simply give it the "new" in service date for when you started using it in the business.
Follow-up screens may or may not ask if you used it for business before the 2020 start date. Simply indicate that you did and follow the prompts.
