To turn on iCloud Drive go to the Settings app on your iOS device or the System Settings on your macOS device. The first time you do this you might need to reboot both devices, or perhaps stop GeoShred and restart it. In some cases you might need to sign in and out of iCloud. See Apple Support for more on that.
IMPORTANT: If you disallowed access to iCloud Drive when GeoShred was first launched, go to the GeoShred menu, Global section, pick Settings and then pick Enable iCloud Drive
GeoShred supports iCloud Drive as a way to synchronize files between devices. When you save a preset or setlist in GeoShred it gets written to the Documents folder.
If iCloud Drive is enabled presets,setlists and audio files are written to GeoShred's iCloud Drive folder.
GeoShred running on other devices will notice that and copy the file to the device's GeoShred Documents folder.
As of this writing, on iOS you may need to put GeoShred in the background then put it back into the foreground to force an iCloud Drive synchronization. The other thing you can do is open Files app. This is a limitation in iCloud Drive which we not in control over.
However, on macOS you don't have to do anything. iCloud Drive will just synch the file without you having to intervene.
Presets, setlists, and audio files with the same names are not copied if their modification dates are identical AND if the sizes of the files are identical. When GeoShred first copies a file from iCloud Drive it forces the copy to have an modified date.
If your devices are on the same network and the connection is good it could take about 5 seconds for the synchronization to happen. Apple is in control of this timing, we can't make it faster.
The reason for this is that many plugin hosts reject MIDI sysex messages.
You can certainly either make changes in multiple places or use GeoShred's Files menu to keep presets and setlists in sync, but it's going to be more work