Don't be surprised if you find the response from FBI less than ideal. The work they do for ATF is not mandatory and therefore gets done as can do and they also don't usually work appeals for other agencies' decisions with the exception of POC states that do FFL checks.
Things can always change, though.
The email I used to get a response was from ATF.gov>who we are>local ATF offices>licensing and other services>federal firearms licensing center. On the right side you'll find the email icon and a phone number. The appeal form was on the FBI web site that appears to deal with denials given to those who 'failed' the background an opportunity to contest, explain, and/or provide documentation that the NICS records are incorrect.
Edited by RogerD, 03 July 2018 - 08:57 AM.