To make a new ending about Ibsen's great play, you would sit down and think about what is mostly likely to happen given what's happened in the final act. You would also decide where you want to focus. Do you want to focus on Torvald, learning to take care of the kids without his wife? Do you want to focus on him at work, when people start to gossip? Do you want to focus on Nora alone? Or Nora the first time they see each other again?
Start with what you think is most likely to happen. I think it is most likely for Torvald to think he wants to change, but for him not to be able to. You might think something different. Then decide how best to dramatize his attempts. (Imagine a camera following him around. Where would it go, and what would it see?)