Assuming a scam - they actually sent a text saying I had joined REST super and to click on link to set up my app. I have not joined REST!!!

Very likely a scam. Received a text from someone claiming to be rest, asking me to update my details in the app. However, they linked a false domain which possibly indicates a phishing attempt (the official domain for rest super is rest.com.au, do not visit or click on any other links). In the text message, they directed me to text this phone number to opt out. I have not messaged this number, and I advise you also not to. They also used my first name, it’s possible that my details were leaked in the data breach in April last year.