If your return has been accepted, you would have to amend your return to add the additional W-2. You should wait until the IRS fully processes your return before you amend, the IRS gets copies of all W-2's so they may send you a letter asking for the additional information.
If your original return gets fully process without the missing W-2 you would then amend your return to add the W-2. The amendment form is not available to sometime in mid to late February, you need to wait until the form is avail to amend your return. Amend returns must be mailed & any refund due with the amended return is sent by check.
If you used TurboTax Online, simply log in to your account and select “Amend a return that was filed and accepted.” If you used our CD/download product, sign back into your return and select “Amend a filed return.” Amended returns can take up to three months for the IRS to process.
https://turbotax.intuit.com/tax-tips/amend-return/10-tax-tips-for-filing-an-amended-return/L2Tt29kwj
Your amended return will take up to 3 weeks after you mailed it to show up on the IRS system. You then can check the status of your amended return
https://www.irs.gov/filing/wheres-my-amended-return
