ITC ON PURCHASE REFUND IN CASH

Hi, no itc can claim on nil rated supplies.

You should reverse the ITC under section 17

Under the provisions of the first proviso to sub-section 3 of Section 54 of the CGST Act a registered person may claim refund of unutilised input credit where the credit has accumulated on account of rate of tax on inputs being higher than the rate of tax on outward supplies, OTHER THAN nil rated or fully exempt supplies.

Hence as your outward supply is nil rated cannot claim refund for accumulated ITC.