after b.u.permission

sir, we have construction business,we constructing residence flat and shop.we purchases raw materials and etc..from registered persons and we claim itc in our 3B returns.we books flats under construction time.some flats sold before b.u.permisson and some sold after b.u.permisson.sir,we want say that those flats sold after b.u.permisson which are tax free,but we taken credit of raw materials which used in those flate so can we should reverse tax credit used in flats sold after b.u.permisson ?please advice us.