If I have already filed my taxes and claimed my second

If you haven't already submitted your return, and you input the wrong amount for the first stimulus you received in the TurboTax Online program, simply type stimulus into the Search box and enter.  Then, if you'll click the link Jump to stimulus, you'll be prompted to enter your amount(s) again.

If you've already submitted your return via e-file, wait to see whether or not it's been accepted. 

• If it's rejected, you can change your return to reflect your proper stimulus.
• If it's accepted, then the IRS will most likely automatically adjust your tax return as a math error, reflecting the correct amount, and you'll receive a notice from the IRS.  If the IRS doesn't contact you about an error, and the refund amount on your return is actually the refund you receive, you'll need to file an amended return.  Please see the TurboTax Help article How to amend (change or correct) a return you already filed for instruction on how to amend your previously-filed tax return.

The IRS requires you to report all relevant stimulus information when you’re filing your return.