You'll need to send your Missouri return by mail. Form MO-WFTC isn't supported by electronic filing.
According to the Form MO-1040 Instructions, you'll need to complete Form MO-WFTC and attach it to Form MO-1040, along with a copy of your federal tax return, including your federal Schedule EIC. If you don't attach these forms, your credit may be disallowed.
The relevant mailing address is shown in both links above, and will also display when you print your Missouri return.
See the TurboTax Help article How do I file my return by mail? for guidance.
See also TurboTax's Tax form availability app, showing the form as not available for electronic filing.
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