For help! How to make recognition component of xcode version?

I am using xcode9, no ios11.2 component and above version,

I manually download "com. Apple. PKG. IPhoneSimulatorSDK12_0-12.0.1.1537588161. DMG" file,

In ~/Library/Caches/com. Apple. Dt. Xcode/Downloads folder,

No ios12 restart xcode, component;

Double-click the install the DMG, restart xcode, add simulator version there is no ios12,

Can help you a great god, and how to operate let xcode can use ios12 simulator