Good day
A seizure is of the most common medical emergencies a dentist can encounter. Usually the dentist tries to minimize the damage the patient can do to himself by moving all harmful equipment away and then monitoring the patient. If the seizure continues for more than 5 min and the dentist is capable, he can give some Diazepam. After the attack, the patient's air way should be monitored, since the patients smooth muscles relax, including the airway muscles.
I would then refer the patient to a medical practitioner for an examination, who will then decide to refer to a neurologist if applicable.