If it is for 2019 you would need to amend your return to add the additional W-2. If it is for 2018 you would still amend your return but you cannot use the Online version.  Amended returns must be mailed.  See the following, it will give you instructions on amending a 2019 or 2018 return.

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

https://ttlc.intuit.com/community/amending/help/how-to-amend-change-or-correct-a-return-you-already-filed/00/25588