You are not able to update your direct deposit information in TurboTax or with the IRS once you have filed your 2019 return. We are still waiting for IRS guidance regarding the direct deposit information for the stimulus payments. We will have more information once the government finalizes the details.
The best option is to make sure the mailing address the IRS has on file for you is correct. Please refer to Update My Information for more information. You can also stay updated by checking back on the following links.
https://turbotax.intuit.com/coronavirus/
https://www.irs.gov/coronavirus