Check this (in french) : https://helpx.adobe.com/fr/pdf/aem-forms/6-3/using-designer.pdf
In SM37, type JDBG (like Job Debug in Background).
Read MoreIn transaction where you can edit code (like SE38, SE80…) :
Refer to the links below :
Building Your First BADI
How to Implement a BADI
How to use filter in a BADI