COVID-19 Economic Stimulus: Amount Received Less Than Authorized

I am married, filed jointly, with three children. I received incorrect amounts for the first and second rounds of the economic stimulus (equivalent to 1 less child). The third-round stimulus package was correct. 

How do I account for the incorrect amounts in the first two stimulus packages using TurboTax Premier to receive the Recovery Rebate Credit? 

The software won't prompt for the Recovery Rebate Credit and states the amount I received is correct; but, it's not. My 2019 taxes were also filed jointly and included three children using TurboTax Deluxe. All three of my children were born prior to 2019.