Observer patter, how to link it with order queue in class diagram?

So I am working on this class diagram, I do get the idea that we need to implement observer pattern with order and customer class, however I couldn't understand what is the best possible way to maintain a relation between order queue ,staff and orders.

Original Question

a web application used to send gifts to your contacts on occasions like birthdays, etc. Application provides a list of gift items that can be sent, such as flowers, cakes, etc. Each gift item has a price. Some gift items are bundle items that combine multiple items into a single item and are offered at a discounted price (e.g. both flowers and cake in a single bundle). Price of a bundle item is the sum of price of all the constituent items, less the discount (specified in percentage). A customer places an order and includes as many items as desired. For each item ordered, quantity needs to be specified. Before the order is placed, application calculates the total order price, taking into account each gift item and its ordered quantity. After the order is placed, both the customer and order fulfillment staff are notified. Customer is notified through email. Order fulfillment staff is notified through a special GUI that lists all pending orders in a First-In- First-Out queue.

a.. Using only the information provided above, develop a complete design-level class diagram by using the following abstractions: Bundle, Customer, Email, GiftItem, Order, OrderItem, and OrderQueue. Your design class diagram must show all relevant attributes, operations, and relationships. It is compulsory to use and explicitly mention all relevant design patterns in your design class diagram (you may add additional classes for this purpose).

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