how can i turn off find my iphone from another device for my iphone?

If you no longer have an iOS device, you need to remotely erase it before you can remove it.

1.In Find My iPhone on iCloud.com, click All Devices, then select the device you want to erase.

If you don’t see All Devices, it’s because you’ve already selected a device. Click the name of the current device in the center of the toolbar to access the Devices list, then select a new device.

2.Erase the device.

Because the device isn’t lost, don’t enter a phone number or message.

If the device is offline, the remote erase begins the next time it’s online. You receive an email when the device is erased.

3.When the device is erased, click Remove from Account.

All your content is erased, and someone else can now activate the device.

You can refer to this Apple Support link for more info: https://support.apple.com/en-ph/guide/icloud/mmfc0eeddd/icloud