Pricing Error in Sales Order - How to Maintain...

I am newbie in SD and having issue, I have a sales order where I enter material and get "Pricing error: Mandatory condition PB00 is missing". Now I know this condition is set for manual entry if it is not found via procedure. But where do I maintain this manual entry, I have checked everywhere and cannot find where I can manually enter or edit the PB00 condition at the item order level?