Before you can get the NDIS, the NDIS need to know some things about your diagnosis and how your disability affects your life. There's a bit on the form they'll give you that your doctor can fill in, or you can give the NDIS copies of reports you've gotten from medical professionals.

You can see more information here: https://www.ndis.gov.au/applying-access-ndis/how-apply/information-support-your-request/providing-evidence-your-disability.