No! You cannot combine tax years. Each tax year must be filed separately. You cannot put 2019 income on a 2020 tax return. You can ONLY enter 2020 income on a 2020 tax return.
If you did not prepare a 2019 state return then you can do that---but it has to be prepared on its own. If you used TurboTax for your 2019 federal return you can download the 2019 software to prepare the 2019 WI return or you can get the paper form from the state and prepare it by hand to mail in. Either way--it cannot be e-filed. A 2019 return must be submitted by mail.
https://ttlc.intuit.com/questions/1900990-how-do-i-file-a-prior-year-tax-return
https://ttlc.intuit.com/community/state-taxes/help/how-do-i-contact-my-state-department-of-revenue/0...
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