Hi there @Bonming!
This is Lana from Shopify.
I understand that you're getting an error when you try to set another bank account because you do not have the old account number. The reason you are asked to verify your old account number is just to prevent payouts being sent to an unauthorized bank account that may have been added accidentally - it is like an extra layer of security.
We can assist you in making this change, but in order to help you out here, we will need to access your Shopify account.
At the moment we are unable to access your account through the community if you require specific support.
Please get in touch with us through this link here so that our team can verify you and see what the next steps are.
Hope this helps and let me know if you need anything else!
I see - so if you cannot remember what the exact numbers that you put in were, you will need to go through through our live support here - we will then be able to look into your account details and help you change your banking information.