Now as per the topic title, you may think this should be hilariously simple, so did I, but something is not going to plan here.
So according to the 2 Degrees website, your DSL (VDSL in my case) password should be "The password you chose at sign up."
And according to other posts on Geekzone, that password should be the SAME password as the password you use to log into your account page.
(https://secure.2degreesbroadband.co.nz/summary)

Now I know what the password is to log into the account page but I do not know if that is the same password as programmed into my 7490, considering I received the modem completely configured.
Because I want to try another modem (NF10W) to see how that works, I of course had to provide my VDSL username and password.

So I did. In the NF10W admin page, I entered my <username>@snap.net.nz account and the SAME password I use to log into my account page with.
But the VDSL connection is not established and the logs show a login failure. Ok, maybe not the same password then? Plugin the 7490 again.

So I go into my account page and see an option to my change my password. I change my password to something else - logout and login onto the page to ensure that all works. Awesome.
I go into my 7490 admin page and just to be certain, I make a backup of all the settings. I then go into the DSL section and change my password to the same password I changed to enter the account page.

"The Internet connection check failed. Log in with the Internet service provider failed. Check the account information you entered (user name and password)."

Thankfully, I managed to "unpaint" myself out of that corner by restoring the settings backup I had made earlier.  I tried this process several times, same results and ending in me restoring the backup again on my 7490.

So I give up - either I do something wrong (most likely), or the password to access my account page IS NOT my VDSL connection password? And if it isn't, where and how can I reset that password?