You can always head down to their comp lab and ask the people there for assistance, just cause you missed that day doesn't mean there won't be help available.
the people down at the computer lab probably wont be helpful in that area. best to go straight to student central....they always help students enrolling in units.
Its easy to enrol. Just follow my 8 simple steps!
Step 1: go to uws.edu.au
Step 2: Click on current students and then click on My Mail (student email)
Step 3: Type in your student ID and password.
Step 4: Click on MySR
Step 5: Under "Course Details", click on enrolment, then click on "Unit Selection"
Step 6: Open up the UWS handbook which you can access from the uws website.
http://handbook.uws.edu.au/hbook/
And look up your course and the unit numbers of the units that you will be studying this semester.
Step 7: Go back to the "Unit Selection" screen that you accessed in Step 5 and type in the unit number/code of the units that you will be studying in the *Unit Code* box that appears towards the bottom of the screen. Click "Get Units"
Step 8: Hey presto, you're all done!
Hope this helps.