I did not put the right amount in for the stimulus check. I put 1200 instead of 2400

If you haven't already submitted your return. You can go back and change the amount. If your return has been submitted and the status of your return is pending, you will need to amend your return when that option is available in Turbo Tax.

I am going to assume your return is submitted, so here are the steps to submit.

1. Log into Turbo Tax 

2. If you reach a landing page, scroll down to the bottom right of the page and look for Amend(change) 2020 return. That option is not there now but will be available sometime after the IRS start accepting electronic filings.

3. Once you start to prepare your amendment Click on Federal Review 
4. Let's make sure you got the right stimulus amount>continue
5. Next screen asks Did you get a stimulus payment? Yes
6. Then a drop down will appear and this is where you will edit your first round payment from $1200 to $2400.
7. If you haven't submitted your return, you can edit by going to federal review and then perform the steps I have outlined above in steps 4-7.