When a return has been filed & accepted, you cannot add direct deposit information.   The IRS is going to give taxpayers the chance to enter their own banking information.  See the following:

The IRS does not have my direct deposit information. What can I do?

In the coming weeks, Treasury plans to develop a web-based portal for individuals to provide their banking information to the IRS online, so that individuals can receive payments immediately as opposed to checks in the mail.

https://www.irs.gov/newsroom/economic-impact-payments-what-you-need-to-know

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If you have not filed a 2019 return, or do not need to file a return, the TurboTax link below, is for anyone who has not filed a 2019 return or if you are not required to file a return,  if you want to qualify for the stimulus money TurboTax just recently setup where you can file a simple return for the stimulus money. See the following, scroll down to  What do I need to do to get my stimulus payment?, then  If you don’t need to file your taxes this year

https://turbotax.intuit.com/stimulus-check/

@adamjwolff  from what we have heard the IRS will not use direct debit information to deposit the stimulus money.  You can check for the IRS portal to add your direct deposit information.

The IRS does not have my direct deposit information. What can I do?

In the coming weeks, Treasury plans to develop a web-based portal for individuals to provide their banking information to the IRS online, so that individuals can receive payments immediately as opposed to checks in the mail.

https://www.irs.gov/newsroom/economic-impact-payments-what-you-need-to-know