Hello, I am a Video Creator and working on upwork from past many years.
As i have been Hiring Voice Talents for many years i would like to mention that for this specific skill i don't look for nicely written cover letters. All i need to see is a Sample Attached with proposal. Some people attached raw files and some attach a properly created audioreel which showcase the voice in many different scenarios. This gives me a clear picture of the persons skills.
My suggestion is to focus on your work samples and use a simple vocer letter to convince clients. A nicely writtern letter will definitely add value to your proposal though.
re: " understand your message, For example, I have a job I want to apply to this job. For my understanding please write a cover letter for this job."
You have asked the Community Forum participants to write a cover letter for a job you want to apply to.
I can assure you that this is not how things work on Upwork.
You need to write your own cover letters.