Report as quickly and timely as possible and practicable.
The means to report should not matter. Ideally reporting can be done through electronic means, such as an electronic form on the intranet of the company. But anything else is suitable. Ensure that in case of a verbal report it is captured by someone professional enough to relay it to the investigation officers.
Make yourself available for follow-up interviews.
Do not report anonymously, people will want to talk to you to learn valuable safety lessons. Have confidence that your name will not be disclosed; it is about learning to prevent the safety event from happening again.