Hi Patrick,
You can use our Syncfusion Window control to add and Edit Appointment to schedule similar to the built-in Add/Edit Dialogue box of Schedule control. Please refer below sample which illustrates how to edit appointment with Syncfusion Window control:
http://www.syncfusion.com/uploads/redirect.aspx?&team=support&file=F94353_Schedule-1433206676.zipPlease try this and let me know if this helps.
Thanks,
Melba