Car Donation - Required Submission of Letter from Charity

I just filed my federal and state taxes electronically. I had donated a car in 2019 to a recognized charity. The car's value was $1095. I did not receive Form 1098-C from the charity, but instead received a letter that documented all the necessary information. TurboTax said when I was preparing my return that I should mail in the charity's letter to the IRS, but when I completed my return I did not receive any information from TurboTax about where to mail it. Where do I need to mail this document, and do I need some sort of cover letter explaining why I am mailing it in separately? What exactly should the cover letter say? Thank you!