If you are the proof owner (or have been given the inviter permission by the proof owner) you can add others into the proof’s workflow.
A green inviter icon next to your name in the workflow means you have the inviter role enabled.
To add a reviewer to the workflow
Open the proof’s info pane by clicking the i icon on the proof tile, or when viewing the proof.
Scroll to the workflow. You can add a reviewer:
Into a past step (standard reviewers only)
Into the current workflow step (any permission)
Into a future workflow step (any permission)
Enter the reviewer’s email address into the Anyone else? field – press the tab or enter key, or click away from the field to add the reviewer.