There are two ways to unlock DLC:
1. Click Install
https://store.steampowered.com/widget/1216690
2. Press the key combination "Win + R" to input:
steam：//install/1216690 or steam://rungameid/1216690，
Press enter, you can get free DLC
There are two ways to unlock DLC:
Build and release context
Recorded Steam release date:
Within one calendar day of this post (UTC). The listed date does not establish an exact launch time.