Yes, you can set a reward discount for leaving a review. Click on the review block in the template editor to open up the Reviews Settings panel on the right.
Check the "Reward with Coupon" box, and set up your coupon's expiration date, value, and type.
That's it! Once this is set up, your customer will receive their unique coupon code once they successfully leave you a review.
You can edit the reviews form, success, and error pages by clicking Reviews --> Edit Page Design.