How to fetch details of User Account Privileged Changed Events

I want to fetch the details of User Account Privilege changed events, as customer is expecting a report on this and they are looking for these particular fields should be there in report. The Fields are "Who made the privilege change, what changes made, when changes are made". We are looking for the way to fetch these 3 fields like who added privilege, when was the privilege added and what particular privilege added.

Please let me know the way how I can achieve this requirement.

Thanks,
Manisha