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If your phone gets slow or doesn't work as it usually does, it may help to restore the factory default settings. All settings and configurations you've made on your phone are deleted.
1. Find "Backup & reset"
Press Advanced settings.
Press Backup & reset.
2. Restore factory default settings
Press Factory data reset.
Press RESET PHONE.
Press RESET PHONE. Wait a moment while the factory default settings are restored. Follow the instructions on the screen to set up your phone and prepare it for use.