No worries! You can just delete the connection and add the correct one:
Go to Settings and then Bank accounts
Click on the little red trash can symbol, next to the account you want to change. If you see anything else related to your bank connection, please remove that as well. Don't forget to press the red trash can in the bottom right corner. This makes sure that the entire bank connection is removed.
Close the Gimi app completely before you start reconnecting the bank accounts. Don't just leave the app – make sure you close it fully.
Open Gimi again and try to connect the bank accounts from scratch.
Please note that if you have more than one bank account connected (to another child) you might need to delete also their connected bank account in order to start over the process.