If you go the the REI Adventures page you should see a small tab off to the right hand side of the site that says "Feedback". If you click the Feedback tab it will have the option to leave a review for your trip that you can make private or public. We appeciate you leaving us a review, and hope you had an amazing time!
@Robf in addition to link @REI-EllisB provided above, after your trip you should have received an email from our Adventures team that contained a link to leave us a review. If, for any reason you don't have that email, please let us know and we can resend it!