ATP Check Based on Firmed Purchase Requisition ?

Dear experts,

Is there a way to do ATP Check based on Firmed Purchase Requisitions ?

We have a process in which the customer wants a better delivery date. We try to met the new date based on components availability from procurement.

The Production Order now has missing parts.

We need a way to make a confirmation based on Firmed Purchase Requisition (after the components availability is confirmed).

Otherwise, ATP based on the PR Processing Status, or delivery confirmation in Purchase Order ?

I need to connect somehow the ATP confirmation with customer confirmation of components.

Thanks,