You will see the discount on checkout.
"3 for 2 on teas offer available in-store and online in Australia only until 11.59pm AEDT Sunday 31 December 2017. Available on selected products only while stocks last. Includes feature teas, loose leaf and teabag gift boxes, everyday refill foils and everyday tins. Excludes tea gift packs. Discount will be automatically applied to lowest value item and reflected in cart at checkout. Customers must purchase promotional items in one transaction to be eligible for the offer. Can be used in conjunction with other sale offers."
Stacks (beautifully) with the amex T2 offer, I believe.