Buy-back form, who do I send it to?

Seems like a newbie question but here goes.

I have decided to participate in the BHP buy-back offer.
The shares were originally brought from Commsec so I'm a CHESS holder.

Problems is, I have no idea how to send the buy-back form off.
The only contacts I can find is https://www.comsec.com.au/Public/ContactUs.aspx

Can I fax the form off?
Can I mail it or do it online? If so Where? Can't seem to find a mailing address or internet form.