iPhone keeps restarting itself every 3 minutes
Since using iTunes to restore the iPhone can't solve this problem, the following method is worth a try:


Restore all settings on your iPhone.
Update all applications or remove potentially conflicting applications
Remove the SIM card from the iPhone and check if it stops restarting
Check and clean the charging port
If you restart when charging, please replace the iPhone battery
Finally, it is recommended to contact Apple officials for the best solution.


https://www.fonecope.com/fix-iphone-keeps-restarting.html