Ask HN: How to report email leak from Google Datastudio?

Hi. After a company I work with send me a link to their Google Datastudio report, I realized that I could access it without identification (visibility is set on User with link). So I thought that I could try random combination to see if there are other reports like this. Of course, after 2 or 3 tries, nothig came up. Then I tried looking directly in Google with a `site:` search. As you can see if you try it, there are a LOT of reporting accessible this way. And I found some with email lists (didn't have to look very far... Took like 30 seconds) and thought : this is a GDPR problem, and I should warn them. As I'm not in security business, what are the best practice to alert the people whose list belongs to ? What to do if I can't identify them ? And, was it a good idea to discuss it here and should I delete this ? Thanks in advance for your answers.