Click 'Rewards' in the navigation bar, and Log In to your account:
Scroll down to 'How to use your points':
If the "Redeem" button i in Blue then you have enough points to redeem your rewards, if it's in Grey then you do not yet have enough points for this reward.
Click 'Redeem' on the Blue Reward you would liek to use on your next purchase. And select "Yes" if you're sure you want to redeem it:
If you are still having difficulty with your code please email firstname.lastname@example.org and our team will happily assist you.
Please include: your name, email address (on your DASH account), the code you were trying to use and the monetary value of the voucher code.