The Contacts Application is baked into the Sierra Operating System and as such can not be reinstalled as an individual Application.
That said, the only was to possible correct the Application is to reboot into Recovery Mode >> Command + R << key and when pressed with several option and choose Reinstall macOS. It would be best to be connected via Ethernet Cable to Router as it is more reliable and steady connection than Wifi.
The Reinstall should download a full version of Sierra and commence the reinstallation process automatically. Further, it should also install any missing or corrupted elements of the OS including Contacts Application.