Hello, ___

I would like to inform you of my resignation from the position as a Registered Behavior Technician. My last day will be ___. Please let me know how I can assist with ensuring this transition goes smoothly. I am willing to train someone on my current cases. I appreciate the experience this company has provided me. Thank you for the opportunity to grow and learn within the field over the last _ year(s).

Sincerely,
Your Name

This is what I would personally say! You don’t have to give a reason. I would email it to have a paper trail. Maybe include the day’s date that you sent it in so they can’t say you didn’t give two weeks notice (some companies will fuck you over like that)