On your Android device, open the Settings app.
Scroll down and tap on Security or Device Administration (depending on your device).
Tap on Unknown sources to enable it.
Open a web browser and navigate to http://androidapksdownloader/chicken-gun-mod-apk/download/.
Download the Chicken Gun Mod APK file that you want to install onto your device and save it to the Downloads folder in your phone's memory card storage area or SD card storage area depending on how your phone is set up.
Once downloaded, open the file from inside of the Downloads folder in File Explorer (Windows) or Finder (Mac).
Tap Install then Agree & Download when prompted by Google Play Store App permissions dialog box, if you see this prompt before opening Chicken Gun Mod APK for installation then you need to re-enable Unknown sources as explained above otherwise skip this step completely by tapping Cancel then Skip instead of installing now because that will automatically uninstall any apps currently installed from unknown sources such as Uber, Facebook Messenger, etc...