Great that you have a clear view on what you need to work on for your second round. It's important that you actually improve on that because they specifically track whether you worked on the feedback they provided.
Based on your description it sounds like you're struggling a bit with structuring. Unfortunately, this is not an easy fix. If you feel this was a problematic part of your first round, I'd perhaps consider postponing the second round and getting some more practice in.
The best way to improve on structuring is not by reading frameworks or books. It's by actually doing good quality cases properly. Aim to go through 40-50 cases and focus only on the initial structuring question. Read the prompt, attempt the answer, then read the suggested solution and try to understand how is it better more sophisticated than yours. You can learn a lot from that.
Additionally, I'd recommend you do a session with a coach. This will accelerate your learning and you'll learn how to create structures organically instead of trying to overlay a framework onto a case.