Hi @Rose_Holt and welcome back to SF
Have you looked at my guide on how top complete your tax return?
There are references to how to fill in cerfa 3916.
You can link to the guide by clicking on this link here.
The guide helps with the 3916 forms whether you are filing on paper or on line.
You might also find some help in this guidance from the impôts.
Hopefully those will help you complete your task.