Please help me correct the following letter
Ask for re-arrangement of date of interview
My name is ABC, canadidate number: 123456. I am delighted to have received your invitation to attend an interview held on 08:30 a.m., 4 April 2013. However, I am sorry to inform you that as I have originally been scheduled to attend an examination at the same time, I am afraid that I am unable to attend your arranged interview. As such, I would like to ask for your assistance in re-arranging the date of interview, desirably later than 4 April 2013, so that I can have an opportunity to talk with you all. If you have any queries, please feel free to contact me at 1234-5678. Thank you for your assistance.
Thank you very much!