If you know you can't make it to a lesson, let the student know as early as possible and suggest another time for the lesson.
Ask student to reschedule the lesson. Students can reschedule any lesson 3 times on their side. When they do, they choose a new time slot in your schedule, so keep it updated.

Generally, try to stick to the schedule you set up, or change it promptly to reflect your current availability. Having lessons rescheduled often can impact how long students stay with you.