can you turn on your find my iPhone from a computer

Welcome to the Apple Community.

You can only locate your device when it is logged into iCloud and 'Find My Phone' is enabled, additionally the device will need to be switched on and connected to a wifi or cellular network.

Unfortunately, you cannot activate iCloud or 'Find My Phone' remotely.

If the device is wiped by you or another, you may not be able to locate the device (although some have reported they can)