I need a professional letter for my job requesting a position as a Part Time for Patient Care Technician to the Critical Care Director.

I need a professional letter for my job requesting a position as a Part Time for Patient Care Technician to the Critical Care Director. I need to be well thought of because I am a student who is going for her last semester. I am a full time who want to become a part time in the same department due to my last semester as a senior.