Dear Samsung Member,
Greetings from Samsung Customer Support!
To resolve auto restart issue please follow below given steps:-
Go to Settings > General management > Reset > Turn off auto start.
If the issue still persist kindly visit the service center for the physical inspection of your device. To check for the nearest Samsung service center kindly click on the link:- https://www.samsung.com/in/support/service-center/
Thank you for writing to Samsung.
Samsung Customer Support