How to use query result as default value in Access

In Access 2003, I design a customer order processing database. There are several tables, Customer (customer code, customer name, dept, salesman, ...), Order (order number, customer code, dept, salesman, ...). How to realize: for order entry, when select one customer, then default value for dept, salesman in the order can be set same as in Customer, but user can also change to other dept or salesman?