how do i turn off find my iphone with a computer

Hello ryen,

Read this article -->

Remove a device from Find My iPhone on iCloud.com - https://support.apple.com/guide/icloud/remove-a-device-mmfc0eeddd/icloud

"If you’re no longer using an iOS device, an Apple Watch, AirPods, or a Mac, you can remove it from Find My iPhone using Find My iPhone on iCloud.com [on a browser on a computer] or your device. When you remove a device, it’s removed from your Find My iPhone Devices list, and if your device has iOS 7 or later, Activation Lock is also turned off."

If instead you mean to turn off Lost Mode:

Turn off Lost Mode on an iPhone, iPad, iPod touch, or Apple Watch

https://support.apple.com/guide/icloud/use-lost-mode-mmfc0f0165/icloud

When you find your lost device, do either of the following to turn off Lost Mode:

- Enter your passcode on the device.

- In Find My iPhone on iCloud.com, click All Devices, then select the device that’s in Lost Mode. Click Lost Mode, click Stop Lost Mode, then click Stop Lost Mode again.