You would amend his return to include the additional W-2s.  Amended returns must be mailed.  Amended returns can take up to 16 weeks to be processed, you may not want to wait to long.

How to amend (change or correct) a return you already filed

https://ttlc.intuit.com/community/amending/help/how-to-amend-change-or-correct-a-return-you-already-...