No third party software needed on mac. The watch mounts as a mass storage device then you just copy the fit files off of it. You may have to check the watch settings and make sure that the USB setting is mass storage mode.

Edit: apparently some Garmin watches only support Media Transfer Protocol:

https://en.wikipedia.org/wiki/Media_Transfer_Protocol

http://webcache.googleusercontent.com/search?q=cache:zx-iTg7...

For these you have to use an MTP client on macOS such as Android File Transfer.