On Earn Rewards (or the review banner on My Profile), click Review on Google or Review on Facebook. This opens the review link and, the first time you click it, records that you started a review and shows a reward amount next to the button. Once claimed the button changes to a checkmark and can't be claimed twice; the reward amount is credited to your wallet after a short delay set by the business (so they have time to confirm the review actually happened) rather than instantly.