Your COROS device and the COROS app do not share the same unit settings. You have to configure the setting on the device and the app separately.
On COROS devices
System > More Settings > Unit > Imperial (feet) | Metric (meters)
On the COROS app
Profile page > Settings > Units > Imperial (feet) | Metric (meters)
Please note, it is not possible to customize different units for different metrics (ex: imperial for distance and metric for elevation).