how to modify install on steam

so i recently got cold war on steam, and i was told it’s possible to modify which parts are installed to save space, but any time i try to look up how this is supposed to work the only thing talked about is how to do it on [battle.net](https://battle.net), when i have it on steam

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when i launch into the game there’s an [option to modify the install](https://imgur.com/lzg8XS4), but whenever i [open it](https://imgur.com/T5b6NZ6) i just get “content management is done through the steam desktop app you will be redirected to the steam desktop app and the game will be closed.” and a cancel button, with no other options. maybe i’m dumb, but i can’t find a single option in steam to do this, nor am i familiar with steam even offering this natively.

any help is appreciated, thanks

edit: solved