How to install older Xcode version from the App Store
if you have previously purchased the xcode version you are interested in, you can download it again from the purchased tab in the app store

and

"There are older versions of Xcode available at the Apple Developer website, but as long as you just use the latest non-beta version of the SDK, you should be fine. E.g. just use Xcode 3.2.5 and iOS 4.2 SDK. The NDA only covers the pre-release versions"

from https://stackoverflow.com/questions/4839526/where-to-download-older-xcode-versions