First click 'Websites', then 'View Websites' on the left hand side of the dash board.
Click 'Edit' next to your website.
Click on the 'Prompt Management' tab.
Once you are here click the 'Add Condition' Button.
Then paste the link that you are trying to apply the exclusion to in the 'Page URL' section.
Pick the prompt that is currently active on your site (custom or default) and set the 'Auto Prompt' tab to 'False'
Now set the Priority to a higher number than your other conditions that you have.
And that's it!
Now the condition is active and your Opt-In prompt will not be displayed on the pages that you have chosen.