If an app has been blocked, you can unblock it by browsing to the file/app in Windows explorer, then right click it and select properties. You can then tick the "unblock" box on the general tab, followed by "ok".
However... if Windows Defender has blocked an app it may be for a good reason. It could be as it bundles a "potentially unwanted application" (i.e. installs another app at the same time to earn money).