I believe the offer is open to everyone.  I had used the Zeelo coach before and that is why I received an e-mail.  However I have just checked and you can access the free offer as follows:

1.  Go to the Zeelo website:  I just entered Zeelo.co into the browser.
2.  The Zeelo home page asks where you are going:  I wrote Bristol Bears
3.  The Bristol v Quins game comes up and you click on it to enter the options for pick up - Stoop or Bracknell.
4.  A cost of £25 per person comes up but enter the promo Quinsaway (as shown on the booking page) and you will be sent a confirmation code to your phone.  Enter the code and the charge resets to £0.
5.  tickets are print at home and all seats you book (not just your own) are free.

The whole thing took no more than 5 min.