Issue Downloading DLC Double Trouble from Steam

Every time I click to download the DLC from the Steam Windows app, it just launches the game and the co op campaign is still not playable. When I click co op campaign button in the game, its just launches steam dlc page in browser for me to download. And when I click on it in the browser window to download, it just asks if I have Steam installed yet, and I am unable to click "yes".

Any ideas? Ive tried everything.

I also launched the properties tab of the original game, but theres no DLC tab for me to toggle the DLC on.

Is there a way to manually install the DLC files?