There’s a Sharing Workouts > iOS > Adding New Workouts from a Mac section on our article here that says you should be able to connect an iOS device to a Mac and transfer the files to the iOS device by placing them in the directory like you currently are then using the following steps to sync them to the device directly
- Use the Finder and select the name of your phone from the left-hand side
- Select the Files tab
- Drag and drop the updated folder under Zwift
- Select Sync