Where do I send the diagnostic files?

Diagnostic files do not need to be sent anywhere,

You can attach them to a post by dragging the file into the textbox you type in or using the upload file button.

But they should only be attached when you are making a bug report or requesting tech support in those forums.

Having one does not mean something bad has happened if that what you’re wondering, they are just a log of game events the devs can use to find out how an issue may have occurred if one does happen.