See Installing the Garmin VIRB Mobile App.
Once you have the application downloaded and have some recorded video footage on your Dash Cam, you will need to set up a Wi-Fi connection between your camera and the app on your phone.
You can view, save, share, or delete dash cam videos and pictures taken from your device on your iPhone using the VIRB® Mobile App. The VIRB Mobile App is a free application that will allow you to easily save or share videos/pictures taken with your Garmin Dash Cam.
Note: iOS version 10.0 or later is required.
See SD Memory Card Sizes for Automotive Devices to ensure you are using a compatible microSD card for recording video.