Open the Apple Support app on your iPhone
Sign in with your Apple ID if prompted
Tap your device under Devices
Tap Device Performance or Diagnostics, if available
Follow the on-screen instructions to start the diagnostic
If prompted, connect to Wi-Fi and keep the device charged
If Apple Support requests a remote diagnostic, follow the link or code they provide
For hardware diagnostics, contact Apple Support or visit an Apple Store/Authorized Service Provider
To run a built-in connection test, open Settings
Tap Privacy & Security
Tap Analytics & Improvements
Review available diagnostic data and logs
For battery and performance checks, open Settings
Tap Battery
Tap Battery Health & Charging
For network diagnostics, open Settings
Tap Wi-Fi or Cellular
Toggle airplane mode on and off
Restart the iPhone if requested during diagnostics