ALL of your W-2’s and/or 1099’s were supposed to be on the same tax return. Remember that next year and do not e-file until you have everything. Now you have to prepare an amended return to add that W-2—and the process will take months.
https://ttlc.intuit.com/questions/2566895-what-does-it-mean-to-amend-a-return
How do I amend my 2019 TurboTax Online return?
A 1040X cannot be e-filed. It must be printed and mailed. It will take about 4 months for the IRS to process an amended return. It is a good idea to use a mailing service that will track it, like UPS or certified mail, so you will know it was received.
Wait about 3 weeks from mailing and you can check the status of your amended return:
https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1
https://www.irs.gov/filing/individuals/amended-returns-form-1040-x/amended-return-frequently-asked-questions
https://ttlc.intuit.com/questions/1908543-do-i-need-to-amend
https://ttlc.intuit.com/questions/3318997-how-does-the-refund-math-work-on-amendments