The payments are the advance child tax credit payments, and the information the IRS uses to make those payments can be updated here:  https://www.irs.gov/credits-deductions/child-tax-credit-update-portal

If you need to amend your return, you can do that from the "Tax Home" screen of TurboTax, after you have logged in to your account.  Simply scroll down to the bottom of the screen, select the year you are amending (2020), and use the options on the right side of the screen to "Amend/Change your return".  Many amended returns can be electronically filed.