Under “calendar” you can view all the appointments you have added. If one of these appointments includes another person, you can send them a message to let them know you’re running late with just two clicks!
To do this, go into your calendar, and select the appointment in question. At the bottom you’ll see four options, one of which is titled “late” and is indicated by an icon of a person running. Press this and a message will be automatically generated with some standard apologetic text that can be edited or sent as is.