Reviewers will see their assigned papers in their Reviewer console and in their Task list. Depending on what method you used to assign Reviewers to papers, they may have already been notified of their assignments:
Manual Assignment from the Program Chair Console
If you assigned reviewers manually using the dropdown in the Program Chair console, they would have received an email for each assignment.
Automatic Assignment Deployed through the Edge Browser
If you deployed an assignment configuration from the edge browser, Reviewers would not have received a notification of their assignments.
Manual Assignment through the Edge Browser
If you use the "Assign" button to add a Reviewer to a paper after having deployed assignments, the Reviewer will receive a notification of their new assignment.