To answer your question ,
What you have is a CASA flight instructor rating with an Aeroplane category endorsement
What you need is a Helicopter category endorsement , connected to that are the training endorsements.
So you have an FAA Helicopter instructor rating , you will need to find a flight school, that teaches instructor ratings, they can give you RPL based on your experience .
Instructor rating come in 3 types
Grade 1 , Grade 2 and grade 3. It's highly likely once passing the training you will be awarded a grade 2 , it's based on hours instructed.( how many hours instructing do you have helicopter ?)
Generally instructor rating are between 30-40 hours in flight and same on ground school.