Can I update my bank information once I have already filed my tax return?

No you can not.

Once you have filed that information has been sent and there is no way to change it.

If you made a minor mistake in the account number, or it was to an old account it won't just get lost. The bank will reject the deposit and the IRS will default to sending a check to the address you have listed on your account.

If you entered the correct information for an account that is still active but you have no access to, you will need to contact that bank.

If the information was wrong, and your address has changed you will need to contact the US postal service and fill out a change of address form.