Dear Sir, 
I am elated to come across this opportunity to serve your organization as an Office Assistant. I have honed my administrative skills and organizational abilities in these last two years,  and I know I have the drive and determination to take on the office assistance role at your company.  Working at your office would be the perfect opportunity for me to use my current skills. 
And I would love the chance to discuss in greater details how I believe I am a perfect fit for this position. Thank you for your time and I'm looking forward to hearing from you.

Sincerely, 
Favour Amobi Ezioma