Final answer:
The best method to reverse work already performed as part of the Lifecycle Event is to configure the rescind activity set with the necessary activities.
Step-by-step explanation:
The best method to reverse work already performed as part of the Lifecycle Event is to configure the rescind activity set with the necessary activities. By configuring the rescind activity set, the HR admin can include the specific activities that need to be reversed in case the new employee decides not to join the company. This provides a systematic way to undo the onboarding work that has already been completed.