The first time you log into your dashboard, there's a popup window with a checkbox and a button that indicate acceptance of the Terms of Service. You'll need to click on that checkbox. If the popup window is too large for your device, you may have to move it around a bit to find the checkbox.
On a related note, entering a device key to use the app constitutes acceptance of the Terms of Service. This means you can start using the app before you ever log into your dashboard. When you do get to the dashboard, all your review requests will be logged under the "Reporting" tab.