How to delete “other” files in music storage?

I accidentally transferred Apple Lossless music files instead of AAC into my Forerunner 970.

i can initially see the files on Garmin Express after transferring.

But once I disconnected the watch and reconnect, the files are no where to be seen on my Mac Garmin Express to delete them. 

Instead, it is showing up as 10G of "other" in my storage.

I’ve connected the watch to a Windows computer and the folders look empty, but that 10G of “other” is still there in storage and unusable.

I have even done a reset to delete all data and settings, and still the same.

Garmin, please help! I’ve written to Garmin support but still no response.