Hi 对方名称, I am terribly sorry I had to break our appointment to take care of a suddent urgent matter.Can we reschedule our appointment to 时间 on 日期 at 地点?We will 动作 when we meet.I look forward to your response.
举例：
Hi Tom, I am terribly sorry I had to break our appointment to take care of a suddent urgent matter.Can we reschedule our appointment to 2 pm this Saturday at the campus center?We will go over our group presentation when we meet.I look forward to your response.