Dear sir,
A very pleasant morning to you. I am writing in response to your advertisement of an Office Assistant needed in your company. 
My name is Koki Tari, I hails from Rivers State. I am a diligent and a hardworking person. Always giving in my best to achieve every desired goal. I wish you can grant me the opportunity to showcase these skillful abilities of mine in your esteemed organization.
Attached herein is my CV. 
Thanks
Yours faithfully, 
Koki Tarilate