Navigate to the RLS popup and now (only if you have the Portal Administrator role) there is a new Spy icon. When you click on it a search box appears. Here you can search through all the Webdashboard users and select one.
When this user is selected, every report (where RLS is enabled) will be accessed with this selected user. A box appears at the bottom that it’s clear you are viewing as this user. Through here you can also close this test mode