Please follow the below steps:
1. Enter the auto-start Settings page of the phone and cancel the auto-run of application that does not need to be on auto-run (some models have no auto-start option).
2. Uninstall some applications that are not commonly used.
3. Check whether the phone has firmware/system push notifications. if so, please upgrade the phone to the latest version. Settings>System>System Update.
4. If it is invalid, please back up the data in the phone (such as contacts, text messages, etc.), and restore the phone to factory settings.