The Client Confirmation and Reminder emails display a button that directs the client to the My Appointments page where the client can change or cancel their booking. Client must be a registered online user to have access to the My Appointments list.

Note, if a client doesn't see their appointments listed in the My Appointments page, it may be that they are logged in to a different profile or have not yet booked their an appointment online from their own profile. Ask the client to confirm they are logged in under the correct email address and that the email matches what you have in your client list.