As I have something urgent to do in Beijing tomorrow, can we put off the meeting to the next week? I'm sorry for the inconvenience caused by it.

解释：

1."我明天去北京有急事"其实是个失约的原由，可翻译为“介于我明天去北京有急事，......”

2.“put off” 推迟的意思，推迟"到" 用 "to "

3.“什么由什么引起 ”译为：“...caused by...”