iPhone is automatically restarting

It sounds like a hardware (battery? digitizer? screen? 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:--> https://locate.apple.com/choose-country-region . 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.

usmanmalik ~ It sounds like the parts weren't replaced by a qualified technician at an authorised service provider. Verify if your provider had access to Apple genuine parts and repair resources:

Repair Provider Verification - Official Apple Support

õ¿õ¬