As a security feature, editing settings is locked while the workflow is active.
Notice that the Setup and Activate Workflow button is unclickable. We've added tooltips to indicate the workflow status and instructions on how to access the settings page. These tooltips appear when hovering your mouse pointer on the Setup and Activate Workflow button or on the info icon beside Workflow Status, as shown:
To access the page for setting up approvers or updating the workflow settings, toggle the activation button off so the Setup and Activate Workflow button becomes clickable, as shown:
Here are related articles on the various settings and setting up reviewers: