When you're talking with your GP, you'll just need to ask them for a Mental Health Care Plan and referral to your someone.health psychologist. They'll know exactly what you're talking about and will have the paperwork required.
Ask your GP to send your MHCP to:
Fax: 02 8367 5101
Post: GPO Box 2126, Sydney NSW 2001
Phone: 1800 491 556
If you've already booked an appointment and know which psychologist you will be seeing you can ask you GP to address it to them, otherwise it can just be addressed to: