How do you get unbreakable armor back in assassins creed 2 if you bought new armor

The unbreakable armor I assume you are talking about is the Armor of Altaïr. If you want to equip the Armor of Altaïr you just go back to your Villa and on the first floor there is a room with mannequins wearing armor. Find the one wearing the Armor of Altaïr and equip it there.