“Swift Language Version” (SWIFT_VERSION) is required to be configured correctly for targets which use Swift

In the navigator selection bar, click the magnifying glass, then search for "SWIFT_VERSION" You will find the places in the project where you can adjust the swift version accordingly.

You can't. XCode 8.2 was the last version to support Swift 2.3. You have to either update to Swift 3 or use Xcode 8.2.

In My case I selected Pod and changed swift version for specific pod. This works for me.