I need to amend my taxes to correct an error, but I noticed the IRS is already sending the return to my bank account. What do I do?

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 tax 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 for amending a 2020 tax return is scheduled to be available on 03/25/2021 (subject to change)

Please understand that the IRS must first approve TT's versions (programming) of the all the tax forms, including the 1040-X amended return, before they can be released to the customer.  In any case, Amended Returns can take 16 weeks or more to process, so please be patient.

You can "return" some of the refund by simply making  a payment on the IRS website.