There are 2 options whereby you can become an AIN in a healthcare facility. Either enroll in an AIN course in TAFE (6 months course) or get into a nursing degree course in Australia. (2nd year and above. If you managed to get into the bridging course, you can work as an AIN immediately.)
You can enroll yourself for a nursing degree, but it does not guarantee you a nursing praciticing cert nor does it guarantee you a new grad position. And yes, if you do not get into bridging program, you will have to start from year 1 again.
Please note that you have to pass IELTS/OET (all 7/B and above) after you graduate from university. If not, you will have to provide evidences of being educated in english for 5 years and above from certain countries. Countries includes: Australia, Canada, Republic of Ireland, South Africa, UK and US. Fail either of these 2 options, you will have issues getting your registration.