Normally, when you create a project, the workflow automatically contains member and reviewer roles for all tasks if the template selected contains this information.
If you have the View people tab and
Edit team members and roles permissions, then all system users, system teams, and member roles are available in the
Members and
Member Roles drop downs even if they were not previously included on the people tab; adding a user to the project workflow automatically adds the user to the people tab.
By contrast, Reviewer and
Reviewer Role cannot be edited directly on the workflow spreadsheet. Add new reviewers and reviewer roles on the Approval popup.