Credit Note of Export

AMBER (Student) (160 Points)

08 June 2020  
Sir
I the month of July 2019 export invoice was raised and goods where dispached. but due to some documentation problem the goods where sezied by Customs Dept. Now the good destroyed in outside country in customs dept.
Now we need to generate credit note invoice of export
My qyestion is which exchange rate should apply Original rate or current rate.
plz advice me