I forgot to add my NEW car I bought to my taxes

[Anita01]

If your return has already been filed and accepted, you would have to amend your return after you receive your original refund.  Amended returns are filed by mail and take the IRS 6-12 weeks to process.

It may not help you to add this change to your return anyway.  The only thing you can deduct for a new car is the sales tax.  Sales tax is just one part of your itemized deductions and you don't receive any benefit from itemizing until your total itemized deductions exceed your standard deduction ($6300 if you filed single).  Also, itemized deductions require the Deluxe version, so you would need to upgrade.

Following are amend instructions.

https://ttlc.intuit.com/replies/5114064