iPhone / iPad keeps restarting - what to do?

You can do that if your iPhone / iPad keeps restarting

A software problem is likely responsible for the frequent reboots of your iPhone or iPad.

To prevent possible data loss during restarts and a reset, you should first create a backup.
To do this, go to the settings of your iOS device. To do this, you have to navigate to your account, select “iCloud” and finally go to “iCloud backup”.
Then tap on “Create backup now”. This process can take some time.
Then return to the overview of the settings and check whether a new software update is available.
To do this, click on "General", "Software Update" and finally on "Download and Install", if a new version is available.
In addition, faulty apps can force your device to restart all the time.
Therefore you should start the App Store and click on “Updates”. Then tap “Update All” to update all apps.
If this still doesn't help and your iPhone or iPad is still restarting, you should reset it to the factory settings. With your backup you can restore all data.
To do this, go to the settings and then to the items "General", "Reset" and "Delete all content and settings".
Then follow the instructions on the display. Here, too, the process can take a long time.
When setting up, you can now select your previously created backup and thus restore all data.
If your iPhone or iPad keeps restarting after this step, you should seek help from Apple Support.