Reversal of GST debit note

I am a manufacturer of zero rated goods.
bought some spare parts and reversed the itc.
now after two months some unused spares returned to supplier, issuing debit note.
GST charged in that debit note.

now my question is,
1. how to deal with this tax liability arised due to the debit note?

a. should be adjusted with current itc and balance amount to be reversed

b. if no itc available , then pay it now and claim subsequently

c. as the itc was never availed at the time of purchase, so no point reversal.