Can we do first expiry first out picking in netsuite wms?

Yes, just make sure your items are set up as Lot Numbered Items.

Thats is already done. How to setup the rule in wms?

Dunno sorry. I just know it's possible. A quick google search brings up an suiteapp that seems directly what you want. https://docs.oracle.com/en/cloud/saas/netsuite/ns-online-help/article_161009052865.html But if it were me, I would work under the assumption that new products are the furthest from expiry, so I would use a FIFO costing method to influence picking. Further to that, you can use NetSuite to make sure you're not allowed to pick expired items https://docs.oracle.com/en/cloud/saas/netsuite/ns-online-help/section_1541443212.html#procedure_1541443217