Check the SDK version command:
xcodebuild -showsdks
Modify the sdk version
$ sudo xcode-select -switch /Applications/Xcode_2.app
Point to your desired xcode path, generally the old xcode is the old sdk
Check the SDK version command:
xcodebuild -showsdks
Modify the sdk version
$ sudo xcode-select -switch /Applications/Xcode_2.app
Point to your desired xcode path, generally the old xcode is the old sdk