This App exports all GPX and FIT files in the "Download" folder. With the "gimporter" ConnectIQ app on the Garmin device courses can be imported. GPX tracks are automatically converted to FIT files.
This App is open source. You are encouraged to extend it.
ConnectIQ App: https://apps.garmin.com/de-DE/apps/de11adc4-fdbb-40b5-86ac-7f93b47ea5bb