It depends on the program flow. If you can get the Customer object which you are attempting to change, you can just invoke the Customer class's methods on the object you retrieve, based on what you are wanting to update about the customer.
Alternatively, you could go the route of creating "update objects", but that will probably be a pretty bloated solution for what you are wanting to do. What I mean by an "update object" is a class like: "CustomerUpdate" which would contain the editable fields for a Customer object. You would create a CustomerUpdate for each update event, and then pass it to the Bank object. The Bank object would then process the CustomerUpdate object based on what values should be updated. This is a solution which is really only used for super-large scale things, so I would not recommend it for your purposes.