Why not have a look on the Alitalia Internet Site?
https://www.alitalia.com/en_it/fly-a...dium-haul.html

If you want to pre-assign seats, you need to get from DL Skypeso the AZ PNR, then if you're lucky you can choose seats on the AZ site. If not, just call AZ to let them assign the seats fr you.