How to rollback Sales Order from Awaiting Billing to previous status?

Our client badly needs help to fix approx $1million of orders that are in the wrong status (like Awaiting Billing already) but still need to be shipped.

Orders are in Awaiting Billing Status and they need to be rolled back to previous state.

Any ideas to work out how to roll them back either manually or systematically are welcome. 

Cause: 
Someone from the business/client side mistakenly ran ESS Release Pause Task for Pause Coordination without Order Number parameter. Consequently, the order lines are now in Awaiting Billing status.