As long as you have been signing in through the same channel (Google or Facebook) and the restaurant is currently signed up for "Menufy Tasty Rewards", you will receive a reward balance approximately 3 hours after your 10th order for that specific Menufy restaurant only.
To redeem it, while placing your next order, log in via the same channel you've been using (Google or Facebook) and on the Menufy Checkout page, check the box "Apply my full $__ reward" found below the payment methods area (see image below). All your rewards balance will be spent on that order. Which means if the order total was $22 and the credit was for $25, the leftover $3 will be thrown out, so make sure to use it all!