So, you want to update the an appointment record created earlier instead of creating a new appointment on date change. I would prefer to use a plugin in this scenario. If you like to use a workflow then you need a certain filter criteria to select the
appointment record you want to update. And there could be a case where there are more than 1 appointment records that need an update. Your required plugin won't be a very complex one and it would provide you flexibility you need to update already created appointment
records.
I hope its helpful.
If this post answers your question, please click "Mark As Answer" on the post and "Mark as Helpful"
Thanks,
Imran Abbasi