Work orders mass update for cost estimate

I want to update the cost (estimate) for all work orders created prior to the work center rate changes.

e.g. WO has no estimated cost for labour. If I hit CTRL+F5 or Calculator button, the costs are recalculated and the estimates for labour are now included.

I need to do this for thousands of work orders. is there any way i can update all at once other than one at a time?

Thanks,

Shah Yan.