There is nothing you can do.
As a matter of security, and during the normal tax season, the IRS will not take requests to change the bank account for a direct deposit. The only thing you can do is cancel the deposit and take a check instead, mailed to the address on your tax return. Imagine your fury, if someone had called the IRS pretending to be you, and got them to change the bank account info so they could steal your refund.
Why would it be any different now? If the IRS took requests to change accounts, some scammer could call them with your name and SSN taken out of your trash can or an identity theft web site, and steal your stimulus.
Bottom line is this is all in the hands of the IRS. There is nothing you or Turbotax can do to change how you receive the stimulus money. If the IRS decides to come up with a secure method of changing payment methods and account numbers, they have to do it.
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