Is it possible to recalculate the Available to Promise (ATP)??

Is it possible to recalculate the Available to Promise (ATP) ?? For one of our items that we manufacture the available to promise isn’t correct as its taking into consideration 2 PO's for that item that were both cancelled in prior periods. Despite the cancelled PO's, the ATP number is still reflective of those two PO's as if they weren’t cancelled. I am trying to get an accurate ATP for this item, how can I force Macola ES to recalculate this figure?? Could I run a MRP Regen even though we aren’t using MRP module?? What are my options for getting an accurate ATP??

Macola ES version 7.6.100”