Your banking information cannot be changed after your tax return has been filed and accepted.
Banking information does not go from TT to the IRS until you file your 2020 tax return and it is accepted. The IRS will begin to accept and process 2020 returns at the end of January 2021.
You enter/change banking information in the FILE section before you file your 2020 return. Changing it on the TurboTax site does not do any good until you file your return and the IRS processes your return. If they manage to start sending out stimulus checks before you can change your information, we hope the IRS provides a way for you to change it with the IRS. If your check goes to a wrong or closed account, it will be sent back to the IRS and then the IRS will mail a check to the address on your tax return.
TurboTax has NO control over your stimulus check, nor can TT track it or tell you when you will receive it. The IRS will use the same banking information for the 2nd stimulus that they used for the first one. If that account (or card) is closed then the stimulus will go back to the IRS and they will mail you a check. See this information from the IRS:
it is POSSIBLE that it will go to the new account, but this is unique situation and TOTALLY conjecture on my part
The IRS will not accept bank account changes at its website due to the risk of fraud from unknown parties. That we know.
But what we don't know is whether the IRS is going to get an updated file of bank accounts from Social Security Administration, which is a trusted source. if they do, it's POSSIBLE the payment goes to the new account.
worst two cases: paper check is mailed and if no payment arrives, then it becomes a tax credit on your 2020 tax return