I would start off by simply talking to your supervisor about a transfer and what you have to do to get said transfer. If they tell you you need to write a letter (not a memo or email) I would follow the standard business letter format, unless your work place typically follows a different template.
Remember to keep it direct, to the point, and formal. You can find templates on Microsoft Word (if you use that word processor) or other examples online. There are so many I can't really suggest one. Remember to use a subject line to inform the recipentant of what your letter is requesting (a transfer).
