You cannot change your banking information for 2019 once your return has been accepted & processed. When you file your 2020 return, you can change your bank information when you go through the steps to file your return.
After the Other Tax Situations section of the 2020 TurboTax program you will be asked about the stimulus payment received or not received in 2020.
After you asked about the stimulus payment & you qualify, you will get the Recovery Rebate Credit (stimulus) on the 2020 federal tax return, Form 1040 Line 30.
If the banking information on your 2019 return is incorrect, then you will automatically switched to receiving a check in the mail. The IRS may or may not offer a portal for tax payers to update their information but so far no information has been given out.
