If you encounter CSAM on the web, just report it to report.cybertip.org and clear your cache. You don’t have to fill out all the detail fields; just give 'em the URL that linked to it.
But mostly, don’t go looking. Don’t try to be a brave vigilante willing to subject yourself to awfulness in order to protect children. That’s not how it works. If you go looking, folks will assume you’re participating.