E invoice in export sales

E invoices should be generated before the shipping bill.
As export is zero rated sale, you can claim tax refund later

I) Gst refund is base on E invoice data.
e.g. I made export as on 1 jan & custom exchange rate was 73. Gst value is 1000 USD. so in INR it is 73000. E invoice is generated with 73000 Gst amount.
now I filled shipping bill on 2 Jan at that time actual custom exchange rate was 73.5 and Gst value mentioned on shipping bill is 73500.

here there is mismatch in E invoice data and shipping bill data.

what to do in this type of scenario?