By default, you can activate your Bricks license key on any website that runs the Bricks theme. That is, if you have not already reached the site limit of your purchased license (https://bricksbuilder.io/pricing/).
To restrict on which WordPress sites your license can be activated, navigate to the “Sites” tab of your Bricks account at https://my.bricksbuilder.io/#sites and scroll to the “Whitelist/blacklist URL” section at the bottom:
There, you can add the URLs of the WordPress sites that you want to allow your license key to be activated at (= whitelist) or disallow your license key to be activated at (= blacklist).
Removing an activated site from the list of sites at https://my.bricksbuilder.io/#sites is not enough to stop it from reappearing. Please make sure to remove the site, and add it to either the white- or blacklist.