激活完还要去测试里兑换资格，预购的人应该可以直接参加测试
Installation Instructions
Open Steam
Click Add a Game > Activate a Product on Steam
Paste your key & click Confirm
Right click on Killing Floor 3 in your Steam Library
Click Properties > Betas
In the “Private Betas” section, enter this password: S4Atp8Jmk2dyrW
Click “Check Code”
Once the code has been entered, select “closed_beta_04” in the “Beta Participation” dropdown window
To confirm that you have the beta installed, make sure the game in your library says “Killing Floor 3 [closed_beta_04]”