CISM is one of the top-ranked credentials into Information Security domain, it requires one to have years of hands-on experience in one of the relevant Information security domains and hence, the exam Is also a tough nut to crack. You need rigorous preparation and for this reason, only self-study at home is no good, you need to go for a formal CISM prep training course from a recognized training provider.

The best CISM training course must have the following inclusions;

It must provide you with flexible training modes.
The training must be interactive and engaging.
You must have approachability to discuss your doubts with the trainer.
Hands-on practice on sample question.
Practice on mock tests and exam simulators is mandatory.
LMS support and engaging reference material must be studies that are relevant and latest.

In our company we usually recommend our IT professionals to seek training from Mercury Solutions as they have more than 98% of exam passing rate and along with that they provide extensive hands-on practice sessions.

The best you could do is talk to the training consultants and get free guidance. This training prep course and certification is worth every bit of your penny spent. So, don't keep brooding, go ahead and all the best!

https://www.mercurysolutions.co/isaca/cism-certified-information-security-manager-certification-training