After you've logged in, click on the tab that says "Community".
At the top of this tab you should see the headings "Message boards", "Teams" & "Statistics".
Click on "Teams".
In the list of "Top Teams", click on BOINC@AUSTRALIA.
There should be a blue link near the top-right of the page that says "JOIN THIS TEAM".
I just tried leaving the team and joining it again and it looks like it's working.
P.S. I believe the url to attach to is https://albertathome.org/
(I just tried removing the project and attaching again using this url and it worked - I'm not getting any messages saying that it's the wrong url)
Edit : I just tried attaching to http://albert.phys.uwm.edu/
and this also appears to work - interesting ...