Clearing of Cenvat Clearing Account

HI All,

Please guide me how can I clear the Cenvat Clearing Account for Year end closing. I tried using F.13 but none of the items are getting cleared since the Assignment field is getting populated by "000000" for MIRO line items instead of PO. No.

Please suggest how can I get the Assignment field filled up by Purchase order# for the entries entered in Past so that I can do clearing. The sort key used is 014 in Cenvat Account.

I have attached the screenshot for your reference. Please suggest.

Thanks 😊