Yellow calendar deletion

If it has been deleted, it means that your mobile phone is already root. If there is no root, there may be one in the phone. You can find it in the settings of application software → "All".

If it has been deleted, you really want to restore it. You have to "restore the factory settings" of your mobile phone. Restoring factory settings is equivalent to returning to the time when you just bought a mobile phone. So, everything in your phone will disappear. So be sure to back up your phone's address book, text messages, call records, photos, music, videos, files and so on in advance. The backup tool can be a mobile phone housekeeper, etc. After backup, restore the factory settings, and after a while, you will have a "brand-new" mobile phone.