It sounds like you're wanting to deduct the sales tax from the vehicle (there is nothing else to deduct on the purchase of a vehicle for an individual). To do so you would need to amend your return (I've included instructions at the bottom of the answer, but be aware that the amend process is not yet available). Note: Adding this to your return will only increase your refund if you itemized your return or if adding the deduction changes you from the standard deduction to itemizing. You will not receive this deduction if you use the standard deduction.
Here is how to tell if you took the standard deduction or itemized - Look at your return. If it is a 1040EZ or 1040-A, you used the standard deduction. Itemized deductions can only be claimed on the regular 1040 form. If you filed a 1040, see if a Schedule A for Itemized Deductions is included with your return. If there is not a Schedule A, you took the Standard Deduction.
Amendment instructions can be found here when they become available for 2017 (early february): https://ttlc.intuit.com/replies/3288565