Hi,
If you are already working in MBB, then each firm will have their enterprise version of ChatGPT that you can use.
But beyond that - at this stage - I would still focus on improving your core problem solving skills which is basically your thinking and reasoning. That is often the most important attribute in junior levels to get right. You can know how to use a tool technically, but if you are not able to deploy it based on strong logic that makes sense, your manager/client won't view that highly.