Initiate a People Review Campaign
You need to create a campaign before you can start it. Consult this help center article dedicated to creating a People Review campaign.
Once you have ensured that all the elements of your campaign are as expected, start your campaign by clicking the + "Start Campaign" button in the header.
If you selected the Manager Preparation option when creating the campaign, a pop-up will appear to inform you that by starting the campaign, a wave of emails will be sent to the managers.