If you have not submitted your return then please follow these steps:

1. Log into TurboTax.
2. After entering all your information click "Federal Review" at the top of your screen. 
3. On the screen "Let's make sure you got the right stimulus amount" click "Continue".
4. You will be asked about the amounts of first round and second round stimulus payments you received.  If you did not receive a payment enter "0".
5. TurboTax will then calculate the amount of stimulus payment remaining that you are still entitled to get. 
6. Any stimulus amount remaining due to you will show as a credit on line 30 of the 1040.

For additional information please see Stimulus FAQ at the end of the TurboTax article.

Thanks for the reply. I don’t actually get the screen “let’s make sure you got the right stimulus amount” after following the instructions.

If you don't get that screen, you may need to log out of your return, clear your cookies and cache, and log back in.  You could also try using a different browser.  Then you should be able to use the instructions above.