If you were the real administrator of the network you were attempting this on, you'd also know how to directly connect to someone else's calendar and get the data you want.
But since you're asking the way that you are, you're neither a paid professional penetration tester doing a job, nor are you the network administrator. So therefore, you're probably doing something you shouldn't be doing.
You're basically asking everyone here to be an accomplice to a crime you wish to commit. That crime, exceeding your authority on a given system.
A third party security audit is the IT equivalent of a colonoscopy. It's long, intrusive, very uncomfortable, and when it's done, you'll have seen things you really didn't want to see, and you'll never forget that you've had one.