A CP11 is an IRS letter that informs you of a problem with your tax return that resulted in the IRS correcting it. If you failed to enter a form 1099-NEC and the IRS discovered it they would recalculate your tax and send you a notice. If you agree that the income was not reported in error, you don't need to file an amended return, you just need to pay the tax due as referenced on the CP11 notice.
If you need to amend your return for some other reason, you will see an option to do that on your home page when you log into TurboTax. Look at the bottom of the page, under Your Tax Return and Documents. Click on the year you want to amend and choose the Amend (Change) option.