Just select 'New game'. Then select the chapter you've just been at. When asked if you want to load a save or use a default character, choose to load a save. By doing so, the game creates a new save game and duplicates your old character.
If you are momentarily stuck in a quest, you can also select a previous chapter while choosing a new game. This way you'll be able to start the quest you are stuck at over again using the new save game. Already finished side quests will also be carried over when using this method.
If you are momentarily stuck in a quest, you can also select a previous chapter while choosing a new game. This way you'll be able to start the quest you are stuck at over again using the new save game. Already finished side quests will also be carried over when using this method.