the letter should contain info on how to appeal. see if thi is something you would want to handle yourself otherwise you'll need a tax pro. for DIY a letter from the dealership signed by a person in authority stating it was a purchase and not a lease should help.
If the IRS adjustment is incorrect, taxpayers can request an appeal through the Office of Appeals by filing a written protest. This process is useful when the dispute involves tax law interpretation. If the issue is factual—providing a backup statement from the seller can strengthen the case. The IRS may also accept a reconsideration request if new evidence emerges after the notice was issued.