Gst regular dealer cancellation

Dear Team,
A regular dealer wants to cancel their GSTN because of closure of business. Stock has been returned to the seller and needs to reverse the ITC before the GSTN cancellation process. Please suggest how to reverse the ITC and in which return form(meaning do they have to reverse the itc during cancellation and in stock details or have to reverse it using gstr-3b).

Please suggest asap anyone.

P.S. ITC has been utiized and reversal will happen using Cash challan, I suppose.