how to restart my iphone 8 plus.

These are the gestures to perform a forced restart of an iPhone 8 or 8+:

Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the power button. Only when the Apple logo appears (it might take 10-20 seconds), release that button (ignore all other screens that might appear, the one with the "slider" to turn the device off included).

If the issue persists, it might be a hardware (battery? other internal component?) failure but we, just users like you, cannot diagnose that issue remotely, sorry.

I suggest that you make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.

zaheer401 wrote:

HI I AM DR ZAHEER ABBAS FROM INDIA , I AM NOT ABLE TO START MY IPHONE 8 PLUS.YESTERDAY IT WAS ON CHARGING MODE AND SUDDENLY IT STARTED BEEPING AND CALLING SOS . LATER IT GOT BLANK. even i was not able to hear properly on this since few days.

Force restart iPhone - Apple Support