Since supply to an SEZ is treated as export and hence the same will have to be shown in 6A Export Invoices and not in 8A, 8B, 8C,8D Nil Rated Supplies in GSTR1.
If you have LUT then select withou payment of tax otherwise with payment of tax and charge IGST.
Supplies to SEZ with LUT / Bond then Show it in Export coloumn...
Without LUT then Show it under B2B section with payment. (You will prepare invoice with IGST. But, You can't collect Tax from Buyer. You ll be pay Your pocket)