If your return has been filed & accepted, you cannot make any changes to your original.  You would have to amend your return to make changes.  Amended returns must be mailed.

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-...

If you have not filed your return, or it was rejected, you can make changes to your return.  Just go back to the Wages & Income section to add the additional W2.