I received an offer for KPMG and my AC was only a couple months ago. This is what I've been telling everyone who's needed help so hopefully, you find it useful, even if it's really long
First of it's really similar to other companies AC, except a bigger group for the group exercise. There were about 16 of us. The group exercise is to design an event but because there are so many people it may be hard to get your point across but you just have to make sure that you make a good relevant point and don't try and dominate the chat. You also have to present your findings as a group to the assessors but don't focus too much on planning the presentation because everyone just has to say a small part, maybe what they thought of, and no one should want to say loads because pressure and they probably know that they need to be a team player.
The group then splits in half, with half doing the written exercise and the other half doing the interview. The written exercise is just an essay where you have to do what you did in the group exercise but on your own and with more statistics. The interview was really relaxed and by the end of mine, me and my interviewer were discussing White Collar and other Netflix shows. Make sure to have questions to ask the interviewer and beforehand just write a list of everything you've done or enjoy doing, like I brought in that I enjoy doing escape rooms and made it relevant by saying teamwork and problem-solving. I also said I enjoy rock climbing and the quick thinking related to it.
The whole day was more relaxed than I expected and went by really quickly. You also get to ask current apprentices what they think, and a tip to make the day more comfortable is to become friends, or at least acquaintances, with the people around you. There were quite a few opportunities where you were just left to talk to each other.
If you have any questions or want any more tips, I'll be glad to help