How to create the command ?
The easiest way is to examine the shortcut you use every time you start LibreOffice. Right-click on it, than "Properties", than copy the "Target" field content. In the example given, it will be "C:\Program Files\LibreOffice 5\program\soffice.exe". Then adjust the syntax to the bash requirements as described before, to get this : "/mnt/c/Program Files/LibreOffice 5/program/soffice.exe" Beware, Unix is case-sensitive, Windows is not.