How to activate Nyakuza Metro Preorder Bonus?

I have pre-ordered the Nyakuza Metro DLC which it just released today, it should contain a Pre-order bonus which says I own it but it is not installed according to my Steam library.

How do I activate/install it?

Solution 1:

So apparently they released it just an hour ago.

Solution 2:

Probably they just forgot to publish it right away or something else is just happening, since I didn't get it aswell even though the DLC is out. The thing is that the pre-order bonus is just a wallpaper, so it might be steam's problem with handling something like that but since I never had a game where it came bundled with wallpapers so