The IRS only uses the bank account from your most recent tax return if you received a tax refund and selected direct deposit.
The only way to change your bank account information with the IRS is to file a 2020 tax return and enter your current bank routing and account number in the File section of the program. That will be sent with your federal tax return when filed.
If there is another stimulus and the IRS sends the payment to an old account, the bank will reject the payment and send the payment back to the IRS. The IRS will then send the payment as a check to the address on the tax return.
