Yes, you can use your 2019 earned income instead of your 2020 income to compute the Earned Income Tax Credit (EIC). Please see What are the qualifications for the Earned Income Credit (EIC or EITC)?

Please follow these steps in TurboTax:

1. Login to your TurboTax Account 
2. Click on the Search box on the top and type "EIC"
3. Click on “Jump to EIC”
4. Answer the questions until you reach the screen "Do you want to use last year’s earned income?"
5. Note your current refund amount using your 2020 earned income at the top of the screen.
6. Click "Yes", enter your "2019 Earned Income" if the field is blank and click "continue".
7. Compare the new refund amount using your 2019 earned income with the previously noted refund amount using your 2020 earned income.
8. If your new refund amount is lower click "back" and then select "No" for the "Do you want to use your 2019 income to calculate this credit instead?" question.

When I followed those instructions, it's telling me that I can't e-file due to a federal issue with my 2020 income??

If you have no income on your 2020 return, it may be causing this error.  Although a return can be e-filed for the Recovery Rebate Credit, for certain taxpayers who have only social security income or SSI, it's not the same for credits like the earned income tax credit (EITC).  This credit undergoes more scrutiny.

For more information about what situations may cause this issue: When a tax return will not e-file