Even if the Design Code(s) assigned to the Part(s) involved in the Workflow requires 2 Activities (and thus to define 2 reviewers), sometimes only 1 activity is visible in the Reviewers tab of a Design Verification Workflow under edition, and it is not possible to define the second one.

It is possible that by mistake, a filter has been applied on the "Activity assignments".

To remove it, click on this icon (Clear Search Criteria) and refresh the Workflow on top of the page.

All activities will now reappear: