Multiple Sale Reports are created automatically, when required, after a Disposition and they can also be created manually. Multiple Sale Reports are Transmitted electronically to the ATF with tracking so you know they have been delivered. You can also Transmit them via email to your CLEO with tracking if they accept them that way.
The Item Types that can be added to Multiple Sale reports can be configured in your Multiple Sale Account Settings.
Both Multiple Sale forms are supported,
Form 3310.4 (Report of Multiple Sale or Other Disposition of Pistols and Revolvers)
Form 3310.12 (Report of Multiple Sale or Other Disposition of Certain Rifles, Only required for type 01 and 02 FFL's in Arizona, California, New Mexico and Texas)
Multiple Sale Reports can be found from the Main Menu by clicking the 'Dispose' button and then on Multiple Sale.
From there you can Create, Edit, Transmit, Delete, Dismiss, and Print your Multiple Sale Reports.
Below is some info from the ATF website
Fact Sheet - Multiple Firearms Sales (May, 2018)
The Gun Control Act (GCA) of 1968 requires federal firearms licensees to report multiple sales or other dispositions of handguns to the same purchaser. In accordance with 18 U.S.C. § 923(g)(3), the sale or disposition of two or more handguns must be reported if they occur at the same time or within five consecutive business days of each other.
In August 2011, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) was authorized by the Office of Management and Budget (OMB) under information collection 1140-0100 (Report of Multiple Sale or Other Disposition of Certain Rifles - ATF Form 3310.12) to initiate similar reporting requirements on the multiple sale or other disposition of certain rifles from licensed firearms dealers in the four border states of Arizona, California, New Mexico and Texas.
The reporting requirements mandate that all federally licensed firearms dealers and pawnbrokers in Arizona, California, New Mexico and Texas, submit to ATF reports of multiple sales or other dispositions of certain rifles to unlicensed individuals when two or more particular kinds of rifles are transferred at the same time or within five consecutive business days of each other. The types of rifles that must be reported are those with the following characteristics: semiautomatic, a caliber greater than .22 (including .223 or 5.56 mm), and the ability to accept detachable magazines.