My 2020 federal return was accepted, but I need to amend the return. I don’t see an option to perform that task in turbo tax in my browser or the app

If the return is accepted you will have to amend your original tax return. An amended return, Form 1040X, can only be printed and mailed to the IRS if the original return was not e-filed. The IRS will take up to 16 weeks or longer to process an amended tax return.

Before starting to amend the tax return, wait for the tax refund to be received or the taxes due to be paid and processed by the IRS.

See this TurboTax support FAQ on amending a tax return originally completed and filed using the 2020 TurboTax online editions - https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-turbotax-online-return/01/27577

The IRS Form 1040-X is scheduled to be available on 02/26/2021 (subject to change)

Slow down.    You cannot amend a tax return that was just accepted.   You have to wait for it to be processed by the IRS.  Trying to send in an amended return while they are still processing the original return could confuse things and delay your refund for months.

Do not try to change anything on your return now.  When you amend, your Form 1040X has to be prepared from the return exactly the way it looked when you filed it originally.   You have to wait.   Once your return has been processed you will complete a Form 1040X   --- which is not yet available --- and submit it to amend the mistakes made when you filed your original return. It takes the IRS at least four months to process an amended return.

The 2020 Form 1040X does not become available until the end of February 2020 (subject to change).