Did the issue occur only after you installed an app? If that's what you did you need to uninstall that app which could be causing your phone to keep on restarting on its own. You might need to go to Safe Mode if your phone immediately restarts every time you reach your home screen.
Here are the steps to put your phone on safe mode:
1. Turn off the smartphone
2. Press and hold the "Power" button
3. At the "Samsung" splash screen, release the "Power" button and instead press and hold "Volume Down"
4. Release the "Volume" button once your phone is done rebooting.
NOTE: After the reboot you should see a "Safe Mode" message in the lower-left area of the screen. source