In assassins creed 2 how do you get back into the animus after you have finished the game

You get in during the credits.
SPOILER ALERT
there is a another pessimal piece of combat as Desmond and everybody. The screen goes black as credits start rolling after the combat and you hop into a vehicle with them and all of the tools. you get back onto the animus inside the vehicle as you head north. you simply start playing as any other open-world game. doing missions, finding feathers. etc.