Just by looking at the appointment, without the need to update it, you can now update the Mileage as follows, click on the Edit button for the Pick Up & Drop Off add-on:
You can now set the mileage for this appointment. Under Qty (quantity) enter the miles, for example, 3.24. The system will then calculate the amount owed based on the $5 per mile this service is set to. So the total would be $16.20:
You can now see the total set: