To move orders from "do not invoice" back to "ready to invoice," you currently need to manually go into each order and each related charge and amend the charge to 'To Invoice' and then save.
Please go into the order and open the charges.
Click on the edit charge button and amend the status to 'To Invoice' (or 'Add to existing invoice' depending on the use case)
This process must be done individually for each order as there is no feature available to change the status in bulk.