Hi,
I don't know about MBB Offer Machine tbh.
But if you want free, you should start off with:
1. Prep Lounge's resources: Case Interview Basics - Honestly, it's got the basic things you need.
2. Then try https://www.preplounge.com/en/management-consulting-cases
Search these types of cases to ensure you cover the basics:
- Profit and loss
- Market size
- Acquisition
(You can see the solutions, so you can see how a structure is constructured).
3. Then try a coach out (I have a free first session)
Good luck :)