The link for support is available in your games library, for each game. There's a button on each game in it's lower right corner. That reveals a menu, and one option is "SUPPORT", which leads to a support page for that specific game.

It's also available when clicking on the game square itself which reveals the files for downloading the game. In that case its the "MORE" button that is the menu with the "SUPPORT" link for that specific game.

Here's the link copied from there, for Riven:
Support for Riven

On that page there's a "CONTACT US" (them, not me) button after all the troubleshooting.