No.  You cannot enter a 2019 W-2 on a 2020 tax return.

You will have to amend the 2019 tax return that was filed to add the 2019 W-2.

See this TurboTax 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/01/123845...

NO NO NO

You cannot put a 2019 W-2 into your 2020 tax return.  If you left it out of your 2019 return then you need to amend your 2019 return.  You absolutely cannot include it with 2020 income.

If your 2019 return has been fully processed, then amend your 2019 return.

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

DO I NEED TO AMEND/

https://ttlc.intuit.com/questions/1908543-do-i-need-to-amend

https://www.irs.gov/filing/individuals/amended-returns-form-1040-x/amended-return-frequently-asked-q...