How can I update the status of an appointment that was mistakenly logged as a no-show?

You have the ability to change the status of an appointment that was mistakenly marked as a No-show to Booked.

From the Schedule view > click on the time of the "no-show" appointment.
To the right of the client's name, click Edit > select Booked from the Status drop-down menu > click Save.

When the appointment status is updated, the cancelled medical will not be automatically associated with the appointment.

Click on the 3 dot menu in the Actions column > select Add medical.
Open the Assign an existing medical tab to select the previously cancelled medical > click Assign medical.

Although you can change the status of an appointment in the past, it is not possible to re-associate a medical with that appointment.