Think the OP is just asking about breakdown cover that comes with the car when it's delivered from new, rather than the relatively new (and seemingly, rare) novelty of a years breakdown cover that comes included when you get your car serviced at a Fiat dealer*
Basically with the first years roadside assistance, on the Fiat's and Alfa's myself & family have bought, we've not needed to do anything or fill anything in. It's just included for 1 year from the date of first registration (3 years on Alfa) and if you need to use it you call CIAO FIAT, the pan-European Fiat Customer Service number, on 00800 3428 0000 (3428 spells FIAT on a phone keypad, to make it easier to remember) & press Option 1 'for immediate roadside assistance'.
It used to transfer you straight through to the AA/RAC but in the last couple of years they've changed to a company that calls out your nearest breakdown provider, a bit like how Green Flag worked/works. They were still pretty decent when my Sister needed them for her Alfa, and I think their should be a booklet (or a section in the warranty & servicing booklet) explaining what's covered, ie home-start, recovery etc.
*participating dealers only, terms, conditions & exclusions apply