Pleaseee help

Hi all.. Please help me with my motivation letter. Here's the story. I wouldlike to apply a job in a national govermnet organization as a national proffesional officer working about hiv/aids. i graduated as medical doctor but my current job is absolutly diferent with the job i wish to apply. I'm now working as an aestetic doctor. I don't know how to make my motivation letter seems to be persuasif and giving more chance to be accepted. And i don't know is it better to write about my current working experience or not. Coz it's contrary between aestatic and hiv. Please help.

Sincerely,

Melouphyou