Dear Hiring Manager,
I am thrilled to put my name in for the Office Assistant Role. I am an independent self-starter. I recently provided a number of services for my clients, including document preparation, maintaining files, copywriting, research, and more administrative skills and services that I believe will add value to your company if given a chance. I am determined to serve your company as perfectly as you see fit. 
I'm ready to start working with your company as soon as possible and I look forward to hearing from you.
Sincerely
Omohafe Iseghohi