Why is my iPhone turning off and Turing on

There are a few possible reasons why your iPhone might be restarting on its own. It could be a software issue, such as a problem with an app or an outdated version of iOS. It could also be a hardware issue, such as a faulty battery or a problem with the device's hardware. If your iPhone keeps restarting, you should try to troubleshoot the problem by following these steps:

1. Make sure your iPhone is up to date by going to Settings > General > Software Update. If an update is available, install it.
2. Restart your iPhone by pressing and holding the power button until the "slide to power off" slider appears. Then, slide the slider to power off your device. Wait a few seconds, then press and hold the power button again to turn your iPhone back on.
3. Check for any app updates by going to the App Store and tapping the "Updates" tab. If any updates are available, install them.
4. Force quit any apps that are causing problems by double-pressing the Home button (or swiping up from the bottom of the screen on an iPhone with Face ID) to bring up the app switcher. Then, swipe left or right to find the app you want to close, and swipe it up and off the screen.
5. If the problem persists, you can try resetting your iPhone by going to Settings > General > Reset and choosing the "Reset All Settings" option. This will reset your iPhone's settings to their default values, but won't delete any of your data.
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If none of these steps help, you may need to contact Apple Support for further assistance. It's also possible that your iPhone has a hardware problem, in which case you may need to take it to an Apple Store or an authorized service provider for repair.

Battery Health may went below 80%. Battery may need a replacement. Check with apple care.