Remove a device in Find My on Mac
If you’re no longer using a device, or you sold it or gave it away, you can remove it from Find My.
In the Find My app
on your Mac, click Devices.In the Devices list, select the device you want to remove.
Click the Info button
on the map, then click Remove This Device.When you remove a device from Find My, Activation Lock is removed immediately and you’re free to give away or sell your device.
You can also remove the Mac you’re using—choose Apple menu 
> System Preferences, click Apple ID, then do one of the following:
Click Overview in the sidebar, then click Sign Out.
Signing out of iCloud turns off all iCloud features on the device. See If you sign out of your Apple ID preferences on Mac.
Click iCloud in the sidebar, then deselect Find My Mac to remove your Mac.
For information about using Find My with other devices, see the user guide for iPhone, iPad, iPod touch, or Apple Watch, or the AirPods Support website.
If you no longer have a device (Mac, iPhone, iPad, iPod touch, or Apple Watch) because you gave it away or sold it, you need to remotely erase it before you can remove it. See Remotely erase a device.