How to get my MCID for MS certificate dated 2005?

Question

Hi, In 2005, my previous employer enrolled me with a Microsoft training company called Comat Training Services to complete Microsoft Office Specialist - Expert on Microsoft Office Excel 2003. I still have both the Comat certificate of achievement and Microsoft Office Specialist certificate dated 2015. There is no serial number given. My current employer is now requesting that I provide the MCID for this course which I have completed in 2005. Kindly advise how can I obtain the MCID. thank you