Diagnostic & Repair

Good morning Nino3526 !

1. Force restart: Try force restarting your iPhone 8 by quickly pressing and releasing the Volume Up button, then quickly pressing and releasing the Volume Down button, and finally holding down the Side (or Power) button until you see the Apple logo. This may help restart the device and resolve any temporary software issues.
2. Connect to iTunes/Finder: If force restarting doesn't resolve the issue, connect your iPhone 8 to a computer with iTunes (on macOS Mojave and earlier) or Finder (on macOS Catalina and later). Your computer may recognize the device and prompt you to update or restore it. Follow the on-screen instructions to proceed with updating or restoring your iPhone.
3. DFU mode: If your iPhone is not recognized by iTunes/Finder, you can try putting it into DFU (Device Firmware Update) mode. This allows your iPhone to be restored from any state. The steps to enter DFU mode vary slightly depending on the iPhone model, so you may need to look up specific instructions for the iPhone 8.
4. Contact Apple Support: If none of the above steps resolve the issue, it's possible that there may be a hardware problem with your iPhone 8. In this case, you may need to contact Apple Support or visit an Apple Authorized Service Provider for further assistance. They can diagnose the issue and provide repair options if necessary.
5. Data recovery: If you're unable to access your messages, pictures, and documents on your iPhone due to the "Diagnostic & Repair" message, you may need to consider data recovery options. This typically involves using specialized software or services to extract data from your iPhone. Keep in mind that data recovery can be complex and may not always be successful.

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With the limited information that you have provided, It is hard to even guess the problems faced by you. 

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