How can I assist in turning off Find My on device that I already shipped?

You have to have the device to turn off Find My, so too late for that. Take a look at the steps under "If you no longer have the phone" to see what you can do. Best to delete the iPhone from your list of devices.

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

Log into icloud.com, find the device, delete it from the list of your devices.

Use Find Devices on iCloud.com - Apple Support

This link will take you directly to the correct web page for the answer to your question:

Remove a device from Find Devices on iCloud.com - Apple Support

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