How do I control the workflow?

Two main options regarding global workflow

1) Matrix Requirements has review labels (Review and Other Workflows)

The review labels can be manually set after a review has been performed and automatically reset after the item was changed.

You can also find more information regarding Design review workflow in out manual.

2) Using an external issue tracking software (e.g. JIRA)

This allows you to set up more elaborate workflows, e.g. to assign users, plan review dates, email notifications, .... See an example here.

If it's to implement a specific workflow within a certain process, some 'gate control' can be applied to manage each approval step of the workflow (See quality gate in the Input fields page of the manual).