You will have to amend the 2019 tax return that was filed to add a W-2
Did you go to the DFAS website for a copy of your W-2 - https://www.dfas.mil/militaryseparations/W2.html
An amended tax return, Form 1040X, can only be printed, signed, dated and mailed by you to the IRS, it cannot be e-filed. The IRS will take up to 4 months to process the amended tax return. Wait until you have received the tax refund or the taxes owed have been paid and processed by the IRS before amending the tax return.
To access your online tax returns sign onto the TurboTax website with the User ID you used to create the account - https://myturbotax.intuit.com/
Scroll down to the bottom of the screen and on the section Your tax returns & documents click on Show. Click on the Year and Click on Amend (change) return
See this TurvrboTax support FAQ for amending a 2019 tax return - https://ttlc.intuit.com/community/tax-topics/help/how-do-i-amend-a-2019-return-in-turbotax/01/1238456#M4600
Once your return is accepted and the finances are settled, you can file an amended return. See how to file an amended return.
You can track your refund from the original return at Where's my refund.
Three weeks after you mail your amended return securely with tracking, visit track an amended return.
@DoninGA is spot on with his advice!