You can update your bank account at any time. However, if your payout is already in transit, it will be paid out to your old bank account and not to the new account.
Stripe creates payouts in advance of their post date to ensure that funds reach your bank account on the date that they are expected. If there is a payout showing in your Dashboard as in transit or paid, updates made to your bank account information will not retroactively apply to these payouts and will only apply to the next payout.
You should contact your old bank to understand what will happen to the funds. You will need to provide the following information: bank account details, date expected, exact amount, and payor (Stripe).
When adding the wrong bank account details, your payout will be sent to this incorrect bank account. To correct this, see: Payout sent to wrong bank account.
If your payout is sent to a closed bank account, it will return to your Stripe account automatically.
You can update your bank account in your dashboard.