why can i not change my bank account info

HOW TO CHANGE OR ENTER BANKING INFORMATION FOR REFUND

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-refund/change-transferred-direct-deposit-information/L77NCbU6D_US_en_US?uid=m6tuh572

You cannot  change banking information while your return is in pending, nor can you change it after the return is accepted.  The IRS does not allow it.

If you haven't filed your return, follow the steps below 

• From your Tax TurboTax Online Home screen Locate Review and File. Click on Finish and File
• You will see the last 3 steps of your return. Click and revisit Step 2 Your refund info. 

** If you are using the phone/tablet app and are having issues with this step, try switching to a computer/laptop. If unable to use a computer, your second-best option will be to switch to a web browser within your phone, and log-in from there instead of the app. 

If you have already filed your return and it has been accepted by the IRS for processing you won’t be able to change it. You need to contact the IRS to try to expedite this process. They will put a hold on the direct deposit and issue a paper check instead. 
 

Click on the link below for additional information
 

What if I entered the wrong bank account for direct deposit?