CFI Bootcamp. They have a great program Mike the owner is the master! Please note that you need to put forth The effort and follow their program and continue to learn;aviation is a life long learning career.
Online Flight Instructor Course California | CFI Training USA. I am a 20 plus year CFII and I was super impressed with the program. It is a lot of work but worth it. I took the ground school as a review when The ACS came about. Definitely recommend in person as the teaching skills learned are spot on.