To enable third-party traffic attribution, log into your YouTube CMS account at cms.youtube.com and click on Account Settings in the top-right corner.
At the bottom of the next page is a link to Third-Party Attribution Settings. Clicking the link will show the options for third-party traffic attribution.
Users have the option to enable traffic to be attributed all to an overall CMS account, or to be broken out by individual channels or groups of channels. Users may also control how their channels are listed in attribution reports.