a letter to send to a person in order to finish job

I'm looking for a freelancer to help me out with a letter that I need to send in order to finish a job. The purpose of the letter is to send a legal letter to finish the job that was started. I'm leaving it up to the freelancer what specific information and details should be included in the letter, but the tone should be assertive. I need this letter finished quickly and the perfect freelancer for the job will have experience writing effective letters with an assertive tone.