All of this happens in the Bullets & Numbering dialog box, shown below. You will definitely want to use paragraph styles for this. My first one is called Chapter title. You will need to begin by changing the List Type to Numbers for all of the levels, and you must both name the List and use the same named list for all Levels. You do this by selecting the List > New List.
I tried very hard to understand your request, but I still don't get it. When exactly do you want that your paragraph restarts at "A"? After a certain paragraph style (title, list or whatever)? In that case, you just need to create a multilevel list. Please be more specific, using screenshot of what you want to achieve at the very end. – Vinny May 18 '17 at 8:17 indesign-numbering