You can purchase a reward you want by exchanging the points you've earned for a reward gift certificate. To purchase a gift certificate from the Home page, click on the plus sign under My Rewards. Once on the Rewards page, you can browse Rewards and click on the Heart icon on the reward you wish to purchase. Once you have purchased the reward gift certificate, you have exchanged your points to purchase that reward, and this cannot be undone.
You should redeem the reward at the merchant location, and show the cashier your screen with the reward code.