Install the most recent version of iOS. If particular problems are causing the issue, an iOS update may be able to fix it. Wirelessly or through iTunes, you may upgrade your smartphone to the current version of iOS. Check for available software updates in Settings-> General-> Software Update if you haven't already. If an update is available for your device, you will receive a notification. Make a backup of your iPhone before downloading and installing the update.

• To update your iPhone SE wirelessly, hit the Download and Install option, then complete the procedure by following the onscreen instructions. To avoid any disruptions in the process, make sure your iPhone is connected to Wi-Fi and hooked into a power source.
• If you want to update your device with iTunes, you'll need a computer (Windows or Mac) with the most recent version   in order to proceed with iOS update installation. After this, check if Find My iPhone is not working problem has been resolved.