xxx can't be opened because it is from an Unidentified developer

For error "xxx can't be opened because it is from an unidentified developer"

Follow the guide to open it.

1. Right Click(or hold Ctrl and click) the file and select Open.
2. Click Open when it asks if you are sure to open it.

If it still doesn't work, try to change the security settings in system preferences.

https://support.apple.com/en-us/HT202491

http://osxdaily.com/2016/09/27/allow-apps-from-anywhere-macos-gatekeeper/