I completed ac syndicate but not seem to be an option to start a new game. Keeps going back to completed game ?
You have to delete your save file and start again, there's no new game button as far as I know.
You can also play the game on a different account.
I know, it's ridiculous. Completely unacceptable. It's easier to start a new game in an MMO, Ubisoft. The heck was this company thinking?