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 your stimulus 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.
If this is in reference to a stimulus payment -
Go to this IRS website - https://www.irs.gov/coronavirus/get-my-payment-frequently-asked-questions
Your payment information cannot be changed. If you don’t get a payment and you are eligible to receive one, it may be claimed on your 2020 tax return as the Recovery Rebate Credit.