You will need to download and print form 706-GS (D-1) from the IRS website and mail it into them.
Mail the form 706-GS (D-1) to:
Department of the Treasury
Internal Revenue Service
Cincinnati, OH 45999
I have found documentation that states Copy A is mailed in. Since I am a distribtee I received copy B. I also discovered that if the Part II, section 3, D (Inclusions ratio) is 0.00 then you do not have to file this form.