Didn't fight Jevil, how exactly do I go back?

So I just got into Deltarune and I'm on Chapter 2. I beat Spamton NEO but haven't fought Queen yet. I was going to fight Jevil in Chapter 1, but I didn't realize I wouldn't be able to backtrack after fighting King. I read on some other posts that it's possible to fight him on another save and get his items, but some people also said you can go back to Chapter 1 on the same save. And then other people said you need to duplicate the save and then go back. And OTHER people said you need to restart the whole thing. Which is true and how do I get his stuff? Should I go back now or after fighting Queen? I have one save file that I've been playing on for Chapters 1 and 2.