Are you the being blocked, or are you trying to access it on a work network ?
Provide them with the URL and the "Reason" code shown on the block screen. They can add the site to an "Allow List" specifically for your user profile. cisco umbrella site blocked
Depending on whether you own the site or are a user, follow these steps: : Are you the being blocked, or are you
Go to Policies > Policy Components > Destination Lists . Are you the being blocked