Which section is it to change stimulus payout amount?

The section to check is at the beginning of the Federal Review. But, to see it, you need to be at the end of Other Tax Situations, first.

 To get there in TurboTax Online, follow these steps:

• In your return, click the Other Tax Situations tab toward the top of the page
• Scroll down to the end and click Let's keep going 
• At Let's make sure you got the right stimulus amount, click Continue
• Be sure to report an amount for each of the stimulus payments as received -- if you did not receive a payment, enter 0 and click Continue

For more information, please refer to: Questions and Answers about the Second Economic Impact Payment which is still getting updates. 

To check your payment status with the IRS, go to: Get My Payment Link.