The interview process already published online. I will only focus on 2 final rounds.
The Assessment Center takes a whole day, from 9am to 7pm. There are 3 rounds, 2 in the morning, then lunch, then 1 in the afternoon.
The 1st rounds is about team work. A case study of a drink company is presented and you have to choose the 2 best suppliers for the company. There are 6 suppliers and 6 critera to judge. Each candidates (6 in total) will be represent a department from the company, who are instructed to favor 1 supplier and disqualify 1 supplier. The point of the test is to evaluate the ability to work in team, respect, reason, protect idea, contributing idea, collaborating skill, not the result (examiners do not even ask about the result, they assess when you work and discuss).
2nd round is about choosing investing plan. 3 investing plan are provided with different context, risk, opportunity. You have to break it down in 25 min, then present your opinion to 2 examiners. Again, it is not about the choice, it is about how you reason and support your claim. The examiner will try to shake your reason, hold on to it (of course with reason, support and claim).
3rd round is about making marketing plan under time pressure. A 10 - page-or-more document provided including email, reference, some data. 55 min is allowed to read and prepare Powerpoint presentation (laptop and mouse provided, and it is shorter than you might think). Then you present your idea, execution plan. The point is to test your creativity and reasoning ability under pressure. Time management is crucial.
Final Meeting with head of function is rather informal. It is all about you up to this point. Note that up to this point, it is not the matter of ability any more, it is the matter of commitment and orientation (you can't show them your career path that is way off track to what they provide, or any sign that you may have low commitment to the program). I suggest the 90-first-day plan to show your commitment. Be serious for what your say.
And good luck!