Final answer:
The medical assistant should acknowledge the message, inquire about any specific tasks or preparations, and update the appointment schedule or inform other staff members about the delay.
Step-by-step explanation:
The medical assistant should inform the provider that they have received the message and understand that the provider will be 20 minutes late to the office. They should also inquire if there are any specific tasks or preparations that need to be done before the provider's arrival. Additionally, the medical assistant should update the appointment schedule or inform any other relevant staff members about the delay.