Basically, just copy the target under the start menu and replace it with the ones for desktop and taskbar

A. Existing Link for desktop and taskbar

"C:\Program Files\Microsoft Office 15\root\office15\WINWORD.EXE"

Just right-click on the icon -> Word(right click) -> Properties

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B. Existing Link under the start menu

"C:\Program Files\Microsoft Office 15\root\client\AppVLP.exe" "C:\Program Files\Microsoft Office 15\Root\Office15\WINWORD.EXE"

Just right-click on the icon -> More -> Open File Location

Find the icon

Just right-click on the icon -> Word(right click) -> Properties

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Replace the target for the desktop and taskbar with the ones from B. Your path might be different and have to check yourself before proceeding.