If a workflow instance has been stopped in Production mode, you can reactivate it.
Invocation of Reactivate displays the Confirm Production Workflow Reactivation dialog ('Are you sure you want to reactivate the '[Workflow Name]' workflow? WARNING: Doing so will cause all activities, including those that have previously completed, to be executed again. In addition, any new records found will be targeted').
Proceeding with the reactivation restarts the workflow instance from the beginning. Any previous contacts are not targeted.
Note that Reactivate is not available at a recurring trigger configured to create a single workflow instance.