- Back up your iPhone.
- Select Settings.
- Select General.
- Tap the Reset button.
- Erase All Settings is the option to choose.
- Enter the right passcode for your device if required.
- To confirm the iPhone reset, tap the choice.
When the reset is finished, your device's factory settings and default options are restored. Set up the relevant settings and parameters, then try to make a test call to see if the problem has been resolved.