Can anyone tell me HOW to use the new "LOOKBACK RULE" and what are those "Rules" for the "RULE. Is there an include no matter what, optional or don't list if using it?

Congress passed a temporary provision. The provision allows taxpayers to use either their 2019 or 2020 income when claiming the Earned Income Tax Credit or Child Tax Credit. Unemployment put some families at risk of missing out or getting a smaller credit as unemployment is not considered "earned income" in the eyes of the IRS. In response, lawmakers are allowing taxpayers to pick which year's income would yield the greatest benefit.