File Form 5329 with your tax return. Do not send it separately unless you've already filed. TurboTax will ask you to provide an explanation which will be included in your e-filing.
Assuming that this was not an RMD to be paid to you as beneficiary of an inherited retirement account, if 2019 was your first RMD year, your 2019 RMD is not yet late and there is no need to file Form 5329. You have until April 1, 2020 to receive your first RMD.
