The only thing that you have to do is include the statement-- I am resigning from my position at your organization. And then I want you to indicate what day.Provide a reason (optional) and then show gratitude. Lastly, use a formal sign-off. Find out who should be the recipient(s). I'm happy to work with you to find an ideal leaving date. I would encourage you to call me as soon as you can so we can come to an agreement. Thank you for understanding in this matter. I'm grateful for the guidance you have provided me throughout my career in the organisation. Please accept this letter as formal notification that I am resigning from my position as XXXX with XXXX.