请懂英文的朋友帮助我翻译以下内容，急用，谢谢！请不要用翻译器

不需要完全逐字照翻，意思达到并符合习惯就可。
请参考我的答案
Something happens here.这句也可以不要

My boss is on a business trip and not coming back yet.
I have to wait here until his back for some issues about working.
Would you please kindly change my ticket to 20th this month?
I am eagerly waiting for your reply. Many thanks

非常抱歉这句没要

I‘m afraid I have to tell you that my flight must be rescheduled to 20th this mouth,since my superviser is out for business and I couldn't go abroad until he's back.I fell awful and I want to know if you are ok with that.
Sorry again and your understanding and instant reply will be sincerely respected.

比较口语化了点，希望能帮到你。

Something unexpected happened, because my boss on business hasn't come
back, I must wait for him and make arrangement for his work and then I can go abroad,
so I need to endorse the ticket to 20th of this month, may I? looking forward to your reply.
I'm seriously sorry, please understand.