Claim refund on itc for exports without payment of igst

Business - export of services only - no local service provided - so adjusted turnvoer is same as export turnover
GST not paid on export of services as issued bond
Input tax credit claimable from office costs like broadband, capital goods etc
Question - how to claim ITC for those months when no export invoices raised as it happens in export of services that not all months will have any turnover. The refund application make the eligible claim as NIL when turnvoer entered as NIL as there is no export invocie but ITC suffered due to usual office costs.