As well, you are likely going to have to manually rearrange the icons on the screen by 'press & drag'. I doubt that there is any 'fix' other than your manually recreating the missing app icons (unless Google / Android / Lenovo has removed them, as sometimes happens as apps no longer are supported by a company & so removed). Then just press & drag to the home screen any icon that you want to replace.
Are the missing icons still installed as apps? You can go to Settings>Apps to check if they are still in the apps list.
